Ultrathin Fluid-Absorbent Cores

ABSTRACT

The present invention relates to ultrathin fluid-absorbent cores comprising a substrate layer, water-absorbent polymer particles and an adhesive, wherein the wet SAP shake out of water-absorbent polymer particles out of the fluid-absorbent core is less than 10% by weight.

The present invention relates to ultrathin fluid-absorbent corescomprising a substrate layer, water-absorbent polymer particles and anadhesive, wherein the wet SAP shake out (SAPLoss) of water-absorbentpolymer particles out of the fluid-absorbent core is less than 10% byweight.

The production of fluid-absorbent articles is described in the monograph“Modern Superabsorbent Polymer Technology”, F. L. Buchholz and A. T.Graham, Wiley-VCH, 1998, pages 252 to 258.

Fluid-absorbent articles such as disposable diapers typically comprisean upper liquid-pervious layer, a lower liquid-impervious layer, and afluid-absorbent core between the upper and the lower layer. Thefluid-absorbent cores typically comprise water-absorbent polymers andfibers.

Ultrathin fluid absorbent cores can be formed by immobilization ofwater-absorbent polymer particles on a nonwoven using hotmelt adhesives,i.e. forming longitudinal strips or discrete spots. Other patterns ofthe water-absorbent polymer particles are also possible.

The preparation of ultrathin fluid-absorbent cores is described, forexample, in EP 1 293 187 A1, U.S. Pat. No. 6,972,011, EP 1 447 066 A1,EP 1 447 067 A1, EP 1 609 448 A1, JP 2004/313580, US 2005/0137085, US2006/0004336, US 2007/0135785 WO 2008/155699 A1, WO 2008/155701 A2, WO2008/155702 A1, WO 2008/155710 A1, WO 2008/155711 A1, WO 2004/071363 A1,US 2003/0181115, WO 2005/097025, US 2007/156108, US 2008/0125735, and WO2008/155722 A2.

The production of water-absorbent polymer particles is likewisedescribed in the monograph “Modern Superabsorbent Polymer Technology”,F. L. Buchholz and A. T. Graham, Wiley-VCH, 1998, pages 71 to 103.Water-absorbent polymer particles are also referred to as“superabsorbent polymers” or “superabsorbents”.

The preparation of water-absorbent polymer particles by polymerizingdroplets of a monomer solution (“dropletization polymerization”) isdescribed, for example, in EP 0 348 180 A1, WO 96/40427 A1, U.S. Pat.No. 5,269,980, DE 103 14 466 A1, DE 103 40 253 A1, DE 10 2004 024 437A1, DE 10 2005 002 412 A1, DE 10 2006 001 596 A1, WO 2008/009580 A1, WO2008/009598 A1, WO 2008/009599 A1, WO 2008/009612 A1, WO 2008/040715 A2,WO 2008/052971, and WO 2008/086976 A1.

It was an object of the present invention to provide ultrathinfluid-absorbent cores having improved properties, i.e. a reduced wet SAPshake out (SAPLoss) of water-absorbent polymer particles.

The object is achieved by fluid-absorbent cores comprising a substratelayer, at least 75% by weight of water-absorbent polymer particles, andan adhesive, wherein the water-absorbent polymer particles have a meansphericity from 0.86 to 0.99 and the wet SAP shake out (SAPLoss) ofwater-absorbent polymer particles out of the fluid-absorbent core isless than 10% by weight.

The fluid-absorbent core comprises preferably at least 80% by weight,more preferably at least 83% by weight, most preferably at least 85% byweight, of water-absorbent polymer particles.

The fluid-absorbent core comprises preferably not more than 15% byweight, more preferably not more than 10% by weight, most preferably notmore than 7% by weight, of the adhesive.

In a preferred embodiment of the present invention a pressure sensitiveadhesive is used that means that no solvent, water or heat is needed toactivate the adhesive. The substrate layer is preferably a nonwovenlayer or a tissue paper. Further, the fluid-absorbent cores can comprisetwo or more layers of water-absorbent polymer particles. Thewater-absorbent polymer particles are preferably placed in discreteregions of the fluid-absorbent core.

The wet SAP shake out (SAPLoss) of water-absorbent polymer particles outof the fluid-absorbent core is preferably less than 8% by weight, morepreferably less than 6% by weight, most preferably less than 5% byweight.

The present invention is based on the finding that the wet SAP shake out(SAPLoss) of water-absorbent polymer particles can be reduced by usingwater-absorbent polymer particles having a specified shape and anadhesive. The water-absorbent polymer particles useful forfluid-absorbent cores according to the present invention are preferablyprepared by dropletization polymerization.

The water-absorbent polymer particles have a mean sphericity ofpreferably from 0.87 to 0.97, more preferably from 0.88 to 0.95, mostpreferably from 0.89 to 0.93.

The water-absorbent polymer particles have a bulk density preferably atleast 0.6 g/cm³, more preferably at least 0.65 g/cm³, most preferably atleast 0.7 g/cm³, and typically less than 1 g/cm³.

The average particle diameter of the water-absorbent particles ispreferably from 250 to 550 μm, more preferably from 350 to 500 μm, mostpreferably from 400 to 450 μm.

The particle diameter distribution is preferably less than 0.7, morepreferably less than 0.65, more preferably less than 0.6.

The ratio of particles having one cavity to particles having more thanone cavity is preferably less than 1.0, more preferably less than 0.7,most preferably less than 0.4. Lower ratios correlated with higher bulkdensities.

Preferred water-absorbent polymer particles are polymer particles havinga centrifuge retention capacity (CRC) of at least 30 g/g, preferably ofat least 32 g/g, more preferably of at least 33 g/g, most preferably ofat least 34 g/g, an absorption under high load (AUHL) of at least 15g/g, preferably of at least 20 g/g, more preferably of at least 22 g/g,most preferably of at least 24 g/g, and a saline flow conductivity (SFC)of at least 5×10⁻⁷ cm³ s/g, preferably of at least 8×10⁻⁷ cm³ s/g, morepreferably of at least 10×10⁻⁷ cm³ s/g, most preferably of at least12×10⁻⁷ cm³ s/g.

Also preferred water-absorbent polymer particles are polymer particleshaving a centrifuge retention capacity (CRC) of at least 20 g/g,preferably of at least 24 g/g, more preferably of at least 26 g/g, mostpreferably of at least 28 g/g, an absorption under high load (AUHL) ofat least 15 gig, preferably of at least 17 g/g, more preferably of atleast 19 g/g, most preferably of at least 20 g/g, and a saline flowconductivity (SFC) of at least 80×10⁻⁷ cm³ s/g, preferably of at least110×10⁻⁷ cm³ s/g, more preferably of at least 130×10⁻⁷ cm² s/g, mostpreferably of at least 150×10⁻⁷ cm³ s/g.

Also preferred water-absorbent polymer particles are polymer particleshaving a centrifuge retention capacity (CRC) of at least 20 g/g,preferably of at least 24 g/g, more preferably of at least 26 g/g, mostpreferably of at least 28 g/g, and a free swell gel bed permeability(GBP) of at least 20 Darcies, preferably of at least 23 Darcies, morepreferably of at least 25 Darcies, most preferably of at least 28Darcies.

The present invention further provides fluid-absorbent articles whichcomprise the inventive fluid-absorbent cores.

DETAILED DESCRIPTION OF THE INVENTION A. Definitions

As used herein, the term “fluid-absorbent composition” refers to acomponent of the fluid-absorbent article which is primarily responsiblefor the fluid handling of the fluid-absorbent article includingacquisition, transport, distribution and storage of body fluids.

As used herein, the term “fluid-absorbent core” refers to afluid-absorbent composition comprising a fibrous material andwater-absorbent polymer particles. The fluid-absorbent core is primarilyresponsible for the fluid handling of the fluid-absorbent articleincluding acquisition, transport, distribution and storage of bodyfluids.

As used herein, the term “layer” refers to a fluid-absorbent compositionwhose primary dimension is along its length and width. It should beknown that the term “layer” is not necessarily limited to single layersor sheets of the fluid-absorbent composition. Thus a layer can compriselaminates, composites, combinations of several sheets or webs ofdifferent materials.

As used herein, the term “x-dimension” refers to the length, and theterm “y-dimension” refers to the width of the fluid-absorbentcomposition, layer, core or article. Generally, the term “x-y dimension”refers to the plane, orthogonal to the height or thickness of thefluid-absorbent composition, layer, core or article.

As used herein, the term “z-dimension” refers to the dimensionorthogonal to the length and width of the fluid-absorbent composition,layer, core or article. Generally, the term “z-dimension” refers to theheight of the fluid-absorbent composition.

As used herein, the term “chassis” refers to fluid-absorbent materialcomprising the upper liquid-pervious layer and the lowerliquid-impervious layer.

As used herein, the term “basis weight” indicates the weight of thefluid-absorbent core per square meter and it includes the chassis of thefluid-absorbent article. The basis weight is determined at discreteregions of the fluid-absorbent core: the front overall average is thebasis weight of the fluid-absorbent core 5.5 cm forward of the center ofthe core to the front distal edge of the core; the insult zone is thebasis weight of the fluid-absorbent core 5.5 cm forward and 0.5 cmbackwards of the center of the core; the back overall average is thebasis weight of the fluid-absorbent core 0.5 cm backward of the centerof the core to the rear distal edge of the core.

As used herein, the term “density” indicates the weight of thefluid-absorbent core per volume and it includes the chassis of thefluid-absorbent article. The density is determined at discrete regionsof the fluid-absorbent core: the front overall average is the density ofthe fluid-absorbent core 5.5 cm forward of the center of the core to thefront distal edge of the core; the insult zone is the density of thefluid-absorbent core 5.5 cm forward and 0.5 cm backwards of the centerof the core; the back overall average is the density of thefluid-absorbent core 0.5 cm backward of the center of the core to therear distal edge of the core.

Further, it should be understood, that the term “upper” refers tofluid-absorbent compositions which are nearer to the wearer of thefluid-absorbent article. Generally, the topsheet is the nearestcomposition to the wearer of the fluid-absorbent article, hereinafterdescribed as “upper liquid-pervious layer”. Contrarily, the term “lower”refers to fluid-absorbent compositions which are away from the wearer ofthe fluid-absorbent article. Generally, the backsheet is the compositionwhich is furthermost away from the wearer of the fluid-absorbentarticle, hereinafter described as “lower liquid-impervious layer”.

As used herein, the term “liquid-pervious” refers to a substrate, layeror laminate thus permitting liquids, i.e. body fluids such as urine,menses and/or vaginal fluids to readily penetrate through its thickness.

As used herein, the term “liquid-impervious” refers to a substrate,layer or a laminate that does not allow body fluids to pass through in adirection generally perpendicular to the plane of the layer at the pointof liquid contact under ordinary use conditions.

Fluid-absorbent articles comprising more than one fluid-absorbent core,in a preferred manner comprising a double-core system including an uppercore and a lower core, hereinafter called “primary core” and “secondarycore”.

As used herein, the term “hydrophilic” refers to the wettability offibers by water deposited on these fibers. The term “hydrophilic” isdefined by the contact angle and surface tension of the body fluids.According to the definition of Robert F. Gould in the 1964 AmericanChemical Society publication “Contact angle, wettability and adhesion”,a fiber is referred to as hydrophilic, when the contact angle betweenthe liquid and the fiber, especially the fiber surface, is less than 90°or when the liquid tends to spread spontaneously on the same surface.

Contrarily, “hydrophobic” refers to fibers showing a contact angle ofgreater than 90° or no spontaneously spreading of the liquid across thesurface of the fiber.

As used herein, the term “section” or “zone” refers to a definite regionof the fluid-absorbent composition.

As used herein, the term “article” refers to any three-dimensional solidmaterial being able to acquire and store fluids discharged from thebody. Preferred articles according to the present invention aredisposable fluid-absorbent articles that are designed to be worn incontact with the body of a user such as disposable fluid-absorbentpantiliners, sanitary napkins, catamenials, incontinence inserts/pads,diapers, training pant diapers, breast pads, interlabial inserts/padsand the like.

As used herein, the term “body fluids” refers to any fluid produced anddischarged by human or animal body, such as urine, menstrual fluids,faeces, vaginal secretions and the like.

B. Water-Absorbent Polymer Particles

The water-absorbent polymer particles are preferably prepared bypolymerizing droplets of a monomer solution comprising

-   a) at least one ethylenically unsaturated monomer which bears acid    groups and may be at least partly neutralized,-   b) at least one crosslinker,-   c) at least one initiator,-   d) optionally one or more ethylenically unsaturated monomers    copolymerizable with the monomers mentioned under a),-   e) optionally one or more water-soluble polymers, and-   f) water,

in a surrounding heated gas phase and flowing the gas cocurrent throughthe polymerization chamber, wherein the temperature of the gas leavingthe polymerization chamber is from 90 to 150° C., the gas velocityinside the polymerization chamber is from 0.1 to 2.5 m/s, and thedroplets are generated by using a droplet plate having a multitude ofbores.

The water-absorbent polymer particles are typically insoluble butswellable in water.

The monomers a) are preferably water-soluble, i.e. the solubility inwater at 23° C. is typically at least 1 g/100 g of water, preferably atleast 5 g/100 g of water, more preferably at least 25 g/100 g of water,most preferably at least 35 g/100 g of water.

Suitable monomers a) are, for example, ethylenically unsaturatedcarboxylic acids such as acrylic acid, methacrylic acid, maleic acid,and itaconic acid. Particularly preferred monomers are acrylic acid andmethacrylic acid. Very particular preference is given to acrylic acid.

Further suitable monomers a) are, for example, ethylenically unsaturatedsulfonic acids such as vinylsulfonic acid, styrenesulfonic acid and2-acrylamido-2-methylpropanesulfonic acid (AMPS).

Impurities may have a strong impact on the polymerization. Preference isgiven to especially purified monomers a). Useful purification methodsare disclosed in WO 2002/055469 A1, WO 2003/078378 A1 and WO 2004/035514A1. A suitable monomer a) is according to WO 2004/035514 A1 purifiedacrylic acid having 99.8460% by weight of acrylic acid, 0.0950% byweight of acetic acid, 0.0332% by weight of water, 0.0203 by weight ofpropionic acid, 0.0001% by weight of furfurals, 0.0001% by weight ofmaleic anhydride, 0.0003% by weight of diacrylic acid and 0.0050% byweight of hydroquinone monomethyl ether.

Polymerized diacrylic acid is a source for residual monomers due tothermal decomposition. If the temperatures during the process are low,the concentration of diacrylic acid is no more critical and acrylicacids having higher concentrations of diacrylic acid, i.e. 500 to 10,000ppm, can be used.

The content of acrylic acid and/or salts thereof in the total amount ofmonomers a) is preferably at least 50 mol %, more preferably at least 90mol %, most preferably at least 95 mol %.

The acid groups of the monomers a) are typically partly neutralized,preferably to an extent of from 25 to 85 mol %, preferentially to anextent of from 50 to 80 mol %, more preferably from 60 to 75 mol %, forwhich the customary neutralizing agents can be used, preferably alkalimetal hydroxides, alkali metal oxides, alkali metal carbonates or alkalimetal hydrogen carbonates, and mixtures thereof. Instead of alkali metalsalts, it is also possible to use ammonia or organic amines, forexample, triethanolamine. It is also possible to use oxides, carbonates,hydrogencarbonates and hydroxides of magnesium, calcium, strontium, zincor aluminum as powders, slurries or solutions and mixtures of any of theabove neutralization agents. Examples for a mixture is a solution ofsodiumaluminate. Sodium and potassium are particularly preferred asalkali metals, but very particular preference is given to sodiumhydroxide, sodium carbonate or sodium hydrogen carbonate, and mixturesthereof. Typically, the neutralization is achieved by mixing in theneutralizing agent as an aqueous solution, as a melt or preferably alsoas a solid. For example, sodium hydroxide with water contentsignificantly below 50% by weight may be present as a waxy materialhaving a melting point above 23° C. In this case, metered addition aspiece material or melt at elevated temperature is possible.

Optionally, it is possible to add to the monomer solution, or tostarting materials thereof, one or more chelating agents for maskingmetal ions, for example iron, for the purpose of stabilization. Suitablechelating agents are, for example, alkali metal citrates, citric acid,alkali metal tatrates, alkali metal lactates and glycolates, pentasodiumtriphosphate, ethylenediamine tetraacetate, nitrilotriacetic acid, andall chelating agents known under the Trilon® name, for example Trilon® C(pentasodium diethylenetriaminepentaacetate), Trilon® D (trisodium(hydroxyethyl)-ethylenediaminetriacetate), and Trilon® M(methylglycinediacetic acid).

The monomers a) comprise typically polymerization inhibitors, preferablyhydroquinone monoethers, as inhibitor for storage.

The monomer solution comprises preferably up to 250 ppm by weight, morepreferably not more than 130 ppm by weight, most preferably not morethan 70 ppm by weight, preferably not less than 10 ppm by weight, morepreferably not less than 30 ppm by weight and especially about 50 ppm byweight of hydroquinone monoether, based in each case on acrylic acid,with acrylic acid salts being counted as acrylic acid. For example, themonomer solution can be prepared using acrylic acid having appropriatehydroquinone monoether content. The hydroquinone monoethers may,however, also be removed from the monomer solution by absorption, forexample on activated carbon.

Preferred hydroquinone monoethers are hydroquinone monomethyl ether(MEHQ) and/or alpha-tocopherol (vitamin E).

Suitable crosslinkers b) are compounds having at least two groupssuitable for crosslinking. Such groups are, for example, ethylenicallyunsaturated groups which can be polymerized by a free-radical mechanisminto the polymer chain and functional groups which can form covalentbonds with the acid groups of monomer a). In addition, polyvalent metalions which can form coordinate bond with at least two acid groups ofmonomer a) are also suitable crosslinkers b).

The crosslinkers b) are preferably compounds having at least twofree-radically polymerizable groups which can be polymerized by afree-radical mechanism into the polymer network. Suitable crosslinkersb) are, for example, ethylene glycol dimethacrylate, diethylene glycoldiacrylate, polyethylene glycol diacrylate, allyl methacrylate,trimethylolpropane triacrylate, triallylamine, tetraallylammoniumchloride, tetraallyloxyethane, as described in EP 0 530 438 A1, di- andtriacrylates, as described in EP 0 547 847 A1, EP 0 559 476 A1, EP 0 632068 A1, WO 93/21237 A1, WO 2003/104299 A1, WO 2003/104300 A1, WO2003/104301 A1 and in DE 103 31 450 A1, mixed acrylates which, as wellas acrylate groups, comprise further ethylenically unsaturated groups,as described in DE 103 314 56 A1 and DE 103 55 401 A1, or crosslinkermixtures, as described, for example, in DE 195 43 368 A1, DE 196 46 484A1, WO 90/15830 A1 and WO 2002/32962 A2.

Suitable crosslinkers b) are in particular pentaerythritol triallylether, tetraallyloxyethane, N,N′-methylenebisacrylamide, 15-tuplyethoxylated trimethylolpropane, polyethylene glycol diacrylate,trimethylolpropane triacrylate and triallylamine.

Very particularly preferred crosslinkers b) are the polyethoxylatedand/or -propoxylated glycerols which have been esterified with acrylicacid or methacrylic acid to give di- or triacrylates, as described, forexample in WO 2003/104301 A1. Di- and/or triacrylates of 3- to 10-tuplyethoxylated glycerol are particularly advantageous. Very particularpreference is given to di- or triacrylates of 1- to 5-tuply ethoxylatedand/or propoxylated glycerol. Most preferred are the triacrylates of 3-to 5-tuply ethoxylated and/or propoxylated glycerol and especially thetriacrylate of 3-tuply ethoxylated glycerol.

The amount of crosslinker b) is preferably from 0.05 to 1.5% by weight,more preferably from 0.1 to 1% by weight, most preferably from 0.3 to0.6% by weight, based in each case on monomer a). On increasing theamount of crosslinker b) the centrifuge retention capacity (CRC)decreases and the absorption under a pressure of 21.0 g/cm² (AUL) passesthrough a maximum.

The initiators c) used may be all compounds which disintegrate into freeradicals under the polymerization conditions, for example peroxides,hydroperoxides, hydrogen peroxide, persulfates, azo compounds and redoxinitiators. Preference is given to the use of water-soluble initiators.In some cases, it is advantageous to use mixtures of various initiators,for example mixtures of hydrogen peroxide and sodium or potassiumperoxodisulfate. Mixtures of hydrogen peroxide and sodiumperoxodisulfate can be used in any proportion.

Particularly preferred initiators c) are azo initiators such as2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride and2,2′-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride, andphotoinitiators such as 2-hydroxy-2-methylpropiophenone and1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one, redoxinitiators such as sodium persulfate/hydroxymethylsulfinic acid,ammonium peroxodisulfate/hydroxymethylsulfinic acid, hydrogenperoxide/hydroxymethylsulfinic acid, sodium persulfate/ascorbic acid,ammonium peroxodisulfate/ascorbic acid and hydrogen peroxide/ascorbicacid, photoinitiators such as1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one, andmixtures thereof. The reducing component used is, however, preferably amixture of the sodium salt of 2-hydroxy-2-sulfinatoacetic acid, thedisodium salt of 2-hydroxy-2-sulfonatoacetic acid and sodium bisulfite.Such mixtures are obtainable as Brüggolite® FF6 and Brüggolite® FF7(Brüggemann Chemicals; Heilbronn; Germany).

The initiators are used in customary amounts, for example in amounts offrom 0.001 to 5% by weight, preferably from 0.01 to 2% by weight, basedon the monomers a).

Examples of ethylenically unsaturated monomers c) which arecopolymerizable with the monomers a) are acrylamide, methacrylamide,hydroxyethyl acrylate, hydroxyethyl methacrylate, dimethylaminoethylacrylate, dimethylaminoethyl methacrylate, dimethylaminopropyl acrylateand diethylaminopropyl methacrylate.

Useful water-soluble polymers d) include polyvinyl alcohol,polyvinylpyrrolidone, starch, starch derivatives, modified cellulosesuch as methylcellulose or hydroxyethylcellulose, gelatin, polyglycolsor polyacrylic acids, polyesters and polyamides, polylactic acid,polyvinylamine, preferably starch, starch derivatives and modifiedcellulose.

For optimal action, the preferred polymerization inhibitors requiredissolved oxygen. Therefore, the monomer solution can be freed ofdissolved oxygen before the polymerization by inertization, i.e. flowingthrough with an inert gas, preferably nitrogen. It is also possible toreduce the concentration of dissolved oxygen by adding a reducing agent.The oxygen content of the monomer solution is preferably lowered beforethe polymerization to less than 1 ppm by weight, more preferably to lessthan 0.5 ppm by weight.

The water content of the monomer solution is preferably less than 65% byweight, preferentially less than 62% by weight, more preferably lessthan 60% by weight, most preferably less than 58% by weight.

The monomer solution has, at 20° C., a dynamic viscosity of preferablyfrom 0.002 to 0.02 Pa·s, more preferably from 0.004 to 0.015 Pa·s, mostpreferably from 0.005 to 0.01 Pa·s. The mean droplet diameter in thedroplet generation rises with rising dynamic viscosity.

The monomer solution has, at 20° C., a density of preferably from 1 to1.3 g/cm³, more preferably from 1.05 to 1.25 g/cm³, most preferably from1.1 to 1.2 g/cm³.

The monomer solution has, at 20° C., a surface tension of from 0.02 to0.06 N/m, more preferably from 0.03 to 0.05 N/m, most preferably from0.035 to 0.045 N/m. The mean droplet diameter in the droplet generationrises with rising surface tension.

Polymerization

The monomer solution is preferably metered into the gas phase to formdroplets, i.e. using a system described in WO 2008/069639 A1 and WO2008/086976 A1. The droplets are generated by means of a droplet plate.

A droplet plate is a plate having a multitude of bores, the liquidentering the bores from the top. The droplet plate or the liquid can beoscillated, which generates a chain of ideally monodisperse droplets ateach bore on the underside of the droplet plate. In a preferredembodiment, the droplet plate is not agitated.

The number and size of the bores are selected according to the desiredcapacity and droplet size. The droplet diameter is typically 1.9 timesthe diameter of the bore. What is important here is that the liquid tobe dropletized does not pass through the bore too rapidly and thepressure drop over the bore is not too great. Otherwise, the liquid isnot dropletized, but rather the liquid jet is broken up (sprayed) owingto the high kinetic energy. The Reynolds number based on the throughputper bore and the bore diameter is preferably less than 2000,preferentially less than 1600, more preferably less than 1400 and mostpreferably less than 1200.

The underside of the droplet plate has at least in part a contact anglepreferably of at least 60°, more preferably at least 75° and mostpreferably at least 90° with regard to water.

The contact angle is a measure of the wetting behavior of a liquid, inparticular water, with regard to a surface, and can be determined usingconventional methods, for example in accordance with ASTM D 5725. A lowcontact angle denotes good wetting, and a high contact angle denotespoor wetting.

It is also possible for the droplet plate to consist of a materialhaving a lower contact angle with regard to water, for example a steelhaving the German construction material code number of 1.4571, and becoated with a material having a larger contact angle with regard towater.

Useful coatings include for example fluorous polymers, such asperfluoroalkoxyethylene, polytetrafluoroethylene,ethylene-chlorotrifluoroethylene copolymers,ethylene-tetrafluoroethylene copolymers and fluorinated polyethylene.

The coatings can be applied to the substrate as a dispersion, in whichcase the solvent is subsequently evaporated off and the coating is heattreated. For polytetrafluoroethylene this is described for example inU.S. Pat. No. 3,243,321.

Further coating processes are to found under the headword “Thin Films”in the electronic version of “Ullmann's Encyclopedia of IndustrialChemistry” (Updated Sixth Edition, 2000 Electronic Release).

The coatings can further be incorporated in a nickel layer in the courseof a chemical nickelization.

It is the poor wettability of the droplet plate that leads to theproduction of monodisperse droplets of narrow droplet size distribution.

The droplet plate has preferably at least 5, more preferably at least25, most preferably at least 50 and preferably up to 750, morepreferably up to 500 bores, most preferably up to 250. The diameter ofthe bores is adjusted to the desired droplet size.

The separation of the bores is usually from 10 to 50 mm, preferably from12 to 40 mm, more preferably from 14 to 35 mm, most preferably from 15to 30 mm. Smaller separations of the bores cause agglomeration of thepolymerizing droplets.

The diameter of the bores is preferably from 50 to 500 μm, morepreferably from 100 to 300 μm, most preferably from 150 to 250 μm.

The temperature of the monomer solution as it passes through the bore ispreferably from 5 to 80° C., more preferably from 10 to 70° C., mostpreferably from 30 to 60° C.

A gas flows through the reaction chamber. The carrier gas is conductedthrough the reaction chamber in cocurrent to the free-falling dropletsof the monomer solution, i.e. from the top downward. After one pass, thegas is preferably recycled at least partly, preferably to an extent ofat least 50%, more preferably to an extent of at least 75%, into thereaction chamber as cycle gas. Typically, a portion of the carrier gasis discharged after each pass, preferably up to 10%, more preferably upto 3% and most preferably up to 1%.

The oxygen content of the carrier gas is preferably from 0.5 to 15% byvolume, more preferably from 1 to 10% by volume, most preferably from 2to 7% by weight.

As well as oxygen, the carrier gas preferably comprises nitrogen. Thenitrogen content of the gas is preferably at least 80% by volume, morepreferably at least 90% by volume, most preferably at least 95% byvolume. Other possible carrier gases may be selected from carbondioxide,argon, xenon, krypton, neon, helium. Any mixture of carrier gases may beused. The carrier gas may also become loaded with water and/or acrylicacid vapors.

The gas velocity is preferably adjusted such that the flow in thereaction chamber is directed, for example no convection currents opposedto the general flow direction are present, and is from 0.1 to 2.5 m/s,preferably from 0.3 to 1.5 m/s, more preferably from 0.5 to 1.2 m/s,even more preferably from 0.6 to 1.0 m/s, most preferably from 0.7 to0.9 m/s.

The gas entrance temperature is controlled in such a way that the gasexit temperature, i.e. the temperature with which the gas leaves thereaction chamber, is from 90 to 150° C., preferably from 100 to 140° C.,more preferably from 105 to 135° C., even more preferably from 110 to130° C., most preferably from 115 to 125° C.

The water-absorbent polymer particles can be divided into threecategories: water-absorbent polymer particles of Type 1 are particleswith one cavity, water-absorbent polymer particles of Type 2 areparticles with more than one cavity, and water-absorbent polymerparticles of Type 3 are solid particles with no visible cavity.

The morphology of the water-absorbent polymer particles can becontrolled by the reaction conditions during polymerization.Water-absorbent polymer particles having a high amount of particles withone cavity (Type 1) can be prepared by using low gas velocities and highgas exit temperatures. Water-absorbent polymer particles having a highamount of particles with more than one cavity (Type 2) can be preparedby using high gas velocities and low gas exit temperatures.

Water-absorbent polymer particles having more than one cavity (Type 2)show an improved mechanical stability.

The reaction can be carried out under elevated pressure or under reducedpressure; preference is given to a reduced pressure of up to 100 mbarrelative to ambient pressure.

The reaction off-gas, i.e. the gas leaving the reaction chamber, may,for example, be cooled in a heat exchanger. This condenses water andunconverted monomer a). The reaction off-gas can then be reheated atleast partly and recycled into the reaction chamber as cycle gas. Aportion of the reaction off-gas can be discharged and replaced by freshgas, in which case water and unconverted monomers a) present in thereaction off-gas can be removed and recycled.

Particular preference is given to a thermally integrated system, i.e. aportion of the waste heat in the cooling of the off-gas is used to heatthe cycle gas.

The reactors can be trace-heated. In this case, the trace heating isadjusted such that the wall temperature is at least 5° C. above theinternal reactor temperature and condensation on the reactor walls isreliably prevented.

Thermal Posttreatment

The residual monomers in the water-absorbent polymer particles obtainedby dropletization polymerization can be removed by a thermalposttreatment in the presence of a gas stream. The residual monomers canbe removed better at relatively high temperatures and relatively longresidence times. What is important here is that the water-absorbentpolymer particles are not too dry. In the case of excessively dryparticles, the residual monomers decrease only insignificantly. Too higha water content increases the caking tendency of the water-absorbentpolymer particles. In order that the water-absorbent polymer particlesdo not dry too rapidly during the thermal posttreatment, the gas flowingin shall already comprise steam.

The thermal posttreatment can be done in an internal and/or an externalfluidized bed. An internal fluidized bed means that the product of thedropletization polymerization is accumulated in a fluidized bed at thebottom of the reaction chamber.

In the fluidized state, the kinetic energy of the polymer particles isgreater than the cohesion or adhesion potential between the polymerparticles.

The fluidized state can be achieved by a fluidized bed. In this bed,there is upward flow toward the water-absorbing polymer particles, sothat the particles form a fluidized bed. The height of the fluidized bedis adjusted by gas rate and gas velocity, i.e. via the pressure drop ofthe fluidized bed (kinetic energy of the gas).

The velocity of the gas stream in the fluidized bed is preferably from0.5 to 2.5 m/s, more preferably from 0.6 to 1.5 m/s, most preferablyfrom 0.7 to 1.0 m/s.

In a more preferred embodiment of the present invention the thermalposttreatment is done in an external mixer with moving mixing tools,preferably horizontal mixers, such as screw mixers, disk mixers, screwbelt mixers and paddle mixers. Suitable mixers are, for example, Beckershovel mixers (Gebr. Lödige Maschinenbau GmbH; Paderborn; Germany), Narapaddle mixers (NARA Machinery Europe; Frechen; Germany), Pflugschar®plowshare mixers (Gebr. Lödige Maschinenbau GmbH; Paderborn; Germany),Vrieco-Nauta Continuous Mixers (Hosokawa Micron BV; Doetinchem; theNetherlands), Processall Mixmill Mixers (Processall Incorporated;Cincinnati; U.S.A.) and Ruberg continuous flow mixers (Gebrüder RubergGmbH & Co KG, Nieheim, Germany). Ruberg continuous flow mixers, Beckershovel mixers and Pflugschar® plowshare mixers are preferred.

The moisture content of the water-absorbent polymer particles during thethermal posttreatment is preferably from 3 to 50% by weight, morepreferably from 6 to 30% by weight, most preferably from 8 to 20% byweight.

The temperature of the water-absorbent polymer particles during thethermal posttreatment is preferably from 60 to 140° C., more preferablyfrom 70 to 125° C., very particularly from 80 to 110° C.

The average residence time in the mixer used for the thermalposttreatment is preferably from 10 to 120 minutes, more preferably from15 to 90 minutes, most preferably from 20 to 60 minutes.

The steam content of the gas is preferably from 0.01 to 1 kg per kg ofdry gas, more preferably from 0.05 to 0.5 kg per kg of dry gas, mostpreferably from 0.1 to 0.25 kg per kg of dry gas.

The thermal posttreatment can be done in a discontinuous external mixeror a continuous external mixer.

The amount of gas to be used in the discontinuous external mixer ispreferably from 0.01 to 5 Nm³/h, more preferably from 0.05 to 2 Nm³/h,most preferably from 0.1 to 0.5 Nm³/h, based in each case on kgwater-absorbent polymer particles.

The amount of gas to be used in the continuous external mixer ispreferably from 0.01 to 5 Nm³/h, more preferably from 0.05 to 2 Nm³/h,most preferably from 0.1 to 0.5 Nm³/h, based in each case on kg/hthroughput of water-absorbent polymer particles.

The other constituents of the gas are preferably nitrogen,carbondioxide, argon, xenon, krypton, neon, helium, air or air/nitrogenmixtures, more preferably nitrogen or air/nitrogen mixtures comprisingless than 10% by volume of oxygen. Oxygen may cause discoloration.

Postcrosslinking

The water-absorbent polymer particles are preferably postcrosslinked forfurther improvement of the properties.

Postcrosslinkers are compounds which comprise groups which can form atleast two covalent bonds with the carboxylate groups of the polymerparticles. Suitable compounds are, for example, polyfunctional amines,polyfunctional amidoamines, polyfunctional epoxides, as described in EP0 083 022 A2, EP 0 543 303 A1 and EP 0 937 736 A2, di- or polyfunctionalalcohols as described in DE 33 14 019 A1, DE 35 23 617 A1 and EP 0 450922 A2, or β-hydroxyalkylamides, as described in DE 102 04 938 A1 andU.S. Pat. No. 6,239,230.

Polyvinylamine, polyamidoamines and polyvinylalcohole are examples ofmultifunctional polymeric postcrosslinkers.

In addition, DE 40 20 780 C1 describes cyclic carbonates, DE 198 07 502A1 describes 2-oxazolidone and its derivatives such as2-hydroxyethyl-2-oxazolidone, DE 198 07 992 C1 describes bis- andpoly-2-oxazolidinones, DE 198 54 573 A1 describes2-oxotetrahydro-1,3-oxazine and its derivatives, DE 198 54 574 A1describes N-acyl-2-oxazolidones, DE 102 04 937 A1 describes cyclicureas, DE 103 34 584 A1 describes bicyclic amide acetals, EP 1 199 327A2 describes oxetanes and cyclic ureas, and WO 2003/31482 A1 describesmorpholine-2,3-dione and its derivatives, as suitable postcrosslinkers.

Particularly preferred postcrosslinkers are ethylene carbonate, mixturesof propylene glycol and 1,4-butanediol, 1,3-propandiole, mixtures of1,3-propandiole and 1,4-butanediole, ethylene glycol diglycidyl etherand reaction products of polyamides and epichlorohydrin.

Very particularly preferred postcrosslinkers are2-hydroxyethyl-2-oxazolidone, 2-oxazolidone and 1,3-propanediol.

In addition, it is also possible to use postcrosslinkers which compriseadditional polymerizable ethylenically unsaturated groups, as describedin DE 37 13 601 A1.

The amount of postcrosslinker is preferably from 0.001 to 2% by weight,more preferably from 0.02 to 1% by weight, most preferably from 0.05 to0.2% by weight, based in each case on the polymer.

Polyvalent cations are preferably applied to the particle surface inaddition to the postcrosslinkers before, during or after thepostcrosslinking.

The polyvalent cations are, for example, divalent cations such as thecations of zinc, magnesium, calcium, iron and strontium, trivalentcations such as the cations of aluminum, iron, chromium, rare earths andmanganese, tetravalent cations such as the cations of titanium andzirconium, and also mixtures thereof. Possible counterions are chloride,bromide, sulfate, hydrogensulfate, carbonate, hydrogencarbonate,nitrate, hydroxide, phosphate, hydrogenphosphate, dihydrogenphosphateand carboxylate, such as acetate, glycolate, tartrate, formiate,propionate, and lactate, and also mixtures thereof. Aluminum sulfate,aluminum acetate, and aluminum lactate are preferred. Apart from metalsalts, it is also possible to use polyamines and/or polymeric amines aspolyvalent cations. A single metal salt can be used as well as anymixture of the metal salts and/or the polyamines above.

The amount of polyvalent cation used is, for example, from 0.001 to 1.5%by weight, preferably from 0.005 to 1% by weight, more preferably from0.02 to 0.8% by weight, based in each case on the polymer.

The postcrosslinking is typically performed in such a way that asolution of the postcrosslinker is sprayed onto the hydrogel or the drypolymer particles. After the spraying, the polymer particles coated withthe postcrosslinker are dried thermally and cooled, and thepostcrosslinking reaction can take place either before or during thedrying.

The spraying of a solution of the postcrosslinker is preferablyperformed in mixers with moving mixing tools, such as screw mixers, diskmixers and paddle mixers. Suitable mixers are, for example, horizontalPflugschar® plowshare mixers (Gebr. Lödige Maschinenbau GmbH; Paderborn;Germany), Vrieco-Nauta Continuous Mixers (Hosokawa Micron BV;Doetinchem; the Netherlands), Processall Mixmill Mixers (ProcessallIncorporated; Cincinnati; US) and Ruberg continuous flow mixers(Gebrüder Ruberg GmbH & Co KG, Nieheim, Germany). Ruberg continuous flowmixers and horizontal Pflugschar® plowshare mixers are preferred. Thepostcrosslinker solution can also be sprayed into a fluidized bed.

If an external mixer or an external fluidized bed is used for thermalposttreatment, the solution of the postcrosslinker can also be sprayedinto the external mixer or the external fluidized bed.

The postcrosslinkers are typically used as an aqueous solution. Theaddition of nonaqueous solvent can be used to adjust the penetrationdepth of the postcrosslinker into the polymer particles.

The thermal drying is preferably carried out in contact dryers, morepreferably paddle dryers, most preferably disk dryers. Suitable driersare, for example, Hosokawa Bepex® horizontal paddle driers (HosokawaMicron GmbH; Leingarten; Geimany), Hosokawa Bepex® disk driers (HosokawaMicron GmbH; Leingarten; Germany), Holo-Flite® dryers (Metso MineralsIndustries Inc.; Danville; U.S.A.) and Nara paddle driers (NARAMachinery Europe; Frechen; Germany). Nara paddle driers and, in the caseof using polyfunctional epoxides, Holo-Flite® dryers are preferred.Moreover, it is also possible to use fluidized bed dryers.

The drying can be effected in the mixer itself, by heating the jacket orblowing in warm air. Equally suitable is a downstream dryer, for examplea shelf dryer, a rotary tube oven or a heatable screw. It isparticularly advantageous to mix and dry in a fluidized bed dryer.

Preferred drying temperatures are in the range from 50 to 220° C.,preferably from 100 to 180° C., more preferably from 120 to 160° C.,most preferably from 130 to 150° C. The preferred residence time at thistemperature in the reaction mixer or dryer is preferably at least 10minutes, more preferably at least 20 minutes, most preferably at least30 minutes, and typically at most 60 minutes.

It is preferable to cool the polymer particles after thermal drying. Thecooling is preferably carried out in contact coolers, more preferablypaddle coolers, most preferably disk coolers. Suitable coolers are, forexample, Hosokawa Bepex® horizontal paddle coolers (Hosokawa MicronGmbH; Leingarten; Germany), Hosokawa Bepex® disk coolers (HosokawaMicron GmbH; Leingarten; Germany), Holo-Flite® coolers (Metso MineralsIndustries Inc.; Danville; U.S.A.) and Nara paddle coolers (NARAMachinery Europe; Frechen; Germany). Moreover, it is also possible touse fluidized bed coolers.

In the cooler the polymer particles are cooled to temperatures of in therange from 20 to 150° C., preferably from 40 to 120° C., more preferablyfrom 60 to 100° C., most preferably from 70 to 90° C. Cooling using warmwater is preferred, especially when contact coolers are used.

Coating

To improve the properties, the water-absorbent polymer particles can becoated and/or optionally moistened. The internal fluidized bed, theexternal fluidized bed and/or the external mixer used for the thermalposttreatment and/or a separate coater (mixer) can be used for coatingof the water-absorbent polymer particles. Further, the cooler and/or aseparate coater (mixer) can be used for coating/moistening of thepostcrosslinked water-absorbent polymer particles. Suitable coatings forcontrolling the acquisition behavior and improving the permeability (SFCor GBP) are, for example, inorganic inert substances, such aswater-insoluble metal salts, organic polymers, cationic polymers andpolyvalent metal cations. Suitable coatings for improving the colorstability are, for example reducing agents and anti-oxidants. Suitablecoatings for dust binding are, for example, polyols. Suitable coatingsagainst the undesired caking tendency of the polymer particles are, forexample, fumed silica, such as Aerosil® 200, and surfactants, such asSpan® 20. Preferred coatings are aluminium monoacetate, aluminiumsulfate, aluminium lactate, Brüggolite® FF7 and Span® 20.

Suitable inorganic inert substances are silicates such asmontmorillonite, kaolinite and talc, zeolites, activated carbons,polysilicic acids, magnesium carbonate, calcium carbonate, calciumphosphate, barium sulfate, aluminum oxide, titanium dioxide and iron(II)oxide. Preference is given to using polysilicic acids, which are dividedbetween precipitated silicas and fumed silicas according to their modeof preparation. The two variants are commercially available under thenames Silica FK, Sipernat®, Wessalon® (precipitated silicas) andAerosil® (fumed silicas) respectively. The inorganic inert substancesmay be used as dispersion in an aqueous or water-miscible dispersant orin substance.

When the water-absorbent polymer particles are coated with inorganicinert substances, the amount of inorganic inert substances used, basedon the water-absorbent polymer particles, is preferably from 0.05 to 5%by weight, more preferably from 0.1 to 1.5% by weight, most preferablyfrom 0.3 to 1% by weight.

Suitable organic polymers are polyalkyl methacrylates or thermoplasticssuch as polyvinyl chloride, waxes based on polyethylene or polypropyleneor polyamides or polytetrafluoro-ethylene. Other examples are:styrene-isoprene-styrene block-copolymers or styrene-butadiene-styreneblock-copolymers.

Suitable cationic polymers are polyalkylenepolyamines, cationicderivatives of polyacrylamides, polyethyleneimines and polyquaternaryamines.

Polyquaternary amines are, for example, condensation products ofhexamethylenediamine, dimethylamine and epichlorohydrin, condensationproducts of dimethylamine and epichlorohydrin, copolymers ofhydroxyethylcellulose and diallyldimethylammonium chloride, copolymersof acrylamide and α-methacryloyloxyethyltrimethylammonium chloride,condensation products of hydroxyethylcellulose, epichlorohydrin andtrimethylamine, homopolymers of diallyldimethylammonium chloride andaddition products of epichlorohydrin to amidoamines. In addition,polyquaternary amines can be obtained by reacting dimethyl sulfate withpolymers such as polyethyleneimines, copolymers of vinylpyrrolidone anddimethylaminoethyl methacrylate or copolymers of ethyl methacrylate anddiethylaminoethyl methacrylate. The polyquaternary amines are availablewithin a wide molecular weight range.

However, it is also possible to generate the cationic polymers on theparticle surface, either through reagents which can form a network withthemselves, such as addition products of epichlorohydrin topolyamidoamines, or through the application of cationic polymers whichcan react with an added crosslinker, such as polyamines or polyimines incombination with polyepoxides, polyfunctional esters, polyfunctionalacids or polyfunctional (meth)acrylates.

It is possible to use all polyfunctional amines having primary orsecondary amino groups, such as polyethyleneimine, polyallylamine andpolylysine. The liquid sprayed preferably comprises at least onepolyamine, for example polyvinylamine or a partially hydrolysedpolyvinylformamide.

The cationic polymers may be used as a solution in an aqueous orwater-miscible solvent, as dispersion in an aqueous or water-miscibledispersant or in substance.

When the water-absorbent polymer particles are coated with a cationicpolymer, the use amount of cationic polymer based on the water-absorbentpolymer particles is usually not less than 0.001% by weight, typicallynot less than 0.01% by weight, preferably from 0.1 to 15% by weight,more preferably from 0.5 to 10% by weight, most preferably from 1 to 5%by weight.

Suitable polyvalent metal cations are Mg²⁺, Ca²⁺, Al³⁺, Sc³⁺, Ti⁴⁺,Mn²⁺, Fe^(2+/3°), Co²⁺, Ni²⁺, Cu^(+/2+), Zn²⁺, Y³⁺, Zr⁴⁺, Ag⁺, La³⁺,Ce⁴⁺, Hf⁴⁺ and Au^(+/3+); preferred metal cations are Mg²⁺, Ca²⁺, Al³⁺,Ti⁴⁺, Zr⁴⁺and La³⁺; particularly preferred metal cations are Al³⁺, Ti⁴⁺and Zr⁴⁺. The metal cations may be used either alone or in a mixturewith one another. Suitable metal salts of the metal cations mentionedare all of those which have a sufficient solubility in the solvent to beused. Particularly suitable metal salts have weakly complexing anions,such as chloride hydroxide, carbonate nitrate and sulfate. The metalsalts are preferably used as a solution or as a stable aqueous colloidaldispersion. The solvents used for the metal salts may be water,alcohols, dimethylformamide, dimethyl sulfoxide and mixtures thereofParticular preference is given to water and water/alcohol mixtures, suchas water/methanol, water/isopropanol, water/1,3-propanediole,water/1,2-propandiole/1,4-butanediole or water/propylene glycol.

When the water-absorbent polymer particles are coated with a polyvalentmetal cation, the amount of polyvalent metal cation used, based on thewater-absorbent polymer particles, is preferably from 0.05 to 5% byweight, more preferably from 0.1 to 1.5% by weight, most preferably from0.3 to 1% by weight.

Suitable reducing agents are, for example, sodium sulfite, sodiumhydrogensulfite (sodium bisulfite), sodium dithionite, sulfinic acidsand salts thereof, ascorbic acid, sodium hypophosphite, sodiumphosphite, and phosphinic acids and salts thereof. Preference is given,however, to salts of hypophosphorous acid, for example sodiumhypophosphite, salts of sulfinic acids, for example the disodium salt of2-hydroxy-2-sulfinatoacetic acid, and addition products of aldehydes,for example the disodium salt of 2-hydroxy-2-sulfonatoacetic acid. Thereducing agent used can be, however, a mixture of the sodium salt of2-hydroxy-2-sulfinatoacetic acid, the disodium salt of2-hydroxy-2-sulfonatoacetic acid and sodium bisulfite. Such mixtures areobtainable as Brüggolite® FF6 and Brüggolite® FF7 (Brüggemann Chemicals;Heilbronn; Germany).

The reducing agents are typically used in the form of a solution in asuitable solvent, preferably water. The reducing agent may be used as apure substance or any mixture of the above reducing agents may be used

When the water-absorbent polymer particles are coated with a reducingagent, the amount of reducing agent used, based on the water-absorbentpolymer particles, is preferably from 0.01 to 5% by weight, morepreferably from 0.05 to 2% by weight, most preferably from 0.1 to 1% byweight.

Suitable polyols are polyethylene glycols having a molecular weight offrom 400 to 20000 g/mol, polyglycerol, 3- to 100-tuply ethoxylatedpolyols, such as trimethylolpropane, glycerol, sorbitol and neopentylglycol. Particularly suitable polyols are 7- to 20-tuply ethoxylatedglycerol or trimethylolpropane, for example Polyol TP 70® (Perstorp AB,Perstorp, Sweden). The latter have the advantage in particular that theylower the surface tension of an aqueous extract of the water-absorbentpolymer particles only insignificantly. The polyols are preferably usedas a solution in aqueous or water-miscible solvents.

When the water-absorbent polymer particles are coated with a polyol, theuse amount of polyol, based on the water-absorbent polymer particles, ispreferably from 0.005 to 2% by weight, more preferably from 0.01 to 1%by weight, most preferably from 0.05 to 0.5% by weight.

The coating is preferably performed in mixers with moving mixing tools,such as screw mixers, disk mixers, paddle mixers and drum coater.Suitable mixers are, for example, horizontal Pflugschar® plowsharemixers (Gebr. Lödige Maschinenbau GmbH; Paderborn; Germany),Vrieco-Nauta Continuous Mixers (Hosokawa Micron BV; Doetinchem; theNetherlands), Processall Mixmill Mixers (Processall Incorporated;Cincinnati; US) and Ruberg continuous flow mixers (Gebrüder Ruberg GmbH& Co KG, Nieheim, Germany). Moreover, it is also possible to use afluidized bed for mixing.

Agglomeration

The water-absorbent polymer particles can further selectivily beagglomerated. The agglomeration can take place after the polymerization,the thermal postreatment, the postcrosslinking or the coating.

Useful agglomeration assistants include water and water-miscible organicsolvents, such as alcohols, tetrahydrofuran and acetone; water-solublepolymers can be used in addition.

For agglomeration a solution comprising the agglomeration assistant issprayed onto the water-absorbing polymeric particles. The spraying withthe solution can, for example, be carried out in mixers having movingmixing implements, such as screw mixers, paddle mixers, disk mixers,plowshare mixers and shovel mixers. Useful mixers include for exampleLödige® mixers, Bepex® mixers, Nauta® mixers, Processall® mixers andSchugi® mixers. Vertical mixers are preferred. Fluidized bed apparatusesare particularly preferred.

Combination of Thermal Posttreatment, Postcrosslinking and OptionallyCoating

In a preferred embodiment of the present invention the steps of thermalposttreatment and postcrosslinking are combined in one process step.Such combination allows the use of very reactive postcrosslinkerswithout having any risk of any residual postcrosslinker in the finishedproduct. It also allows the use of low cost equipment and moreover theprocess can be run at low temperatures which is cost-efficient andavoids discoloration and loss of performance properties of the finishedproduct by thermal degradation.

Postcrosslinkers in this particular preferred embodiment are selectedfrom epoxides, aziridines, polyfuntional epoxides, and polyfunctionalaziridines. Examples are ethylene glycol diglycidyl ether, propyleneglycol diglycidyl ether, polyethylene glycol diglycidyl ether,polyglycerol polyglycidyl ether, glycerol polyglycidyl ether, sorbitolpolyglycidyl ether, pentaerythritol polyglycidyl ether. Such compoundsare available for example under the trade name Denacol® (Nagase ChemteXCorporation, Osaka, Japan). These compounds react with the carboxylategroups of the water-absorbent polymers to form crosslinks already atproduct temperatures of less than 160° C.

The mixer may be selected from any of the equipment options cited in thethermal posttreatment section. Ruberg continuous flow mixers, Beckershovel mixers and Pflugschar® plowshare mixers are preferred.

In this particular preferred embodiment the postcrosslinking solution issprayed onto the water-absorbent polymer particles under agitation. Thetemperature of the water-absorbent polymer particles inside the mixer isat least 60° C., preferably at least 80° C., more preferably at least90° C., most preferably at least 100° C., and preferably not more than160° C., more preferably not more than 140° C., most preferably not morethan 115° C. Thermal posttreatment and postcrosslinking are performed inthe presence of a gas stream having a moisture content cited in thethermal posttreatment section.

Following the thermal posttreatment/postcrosslinking the water-absorbentpolymer particles are dried to the desired moisture level and for thisstep any dryer cited in the postcrosslinking section may be selected.However, as only drying needs to be accomplished in this particularpreferred embodiment it is possible to use simple and low cost heatedcontact dryers like a heated screw dryer, for example a Holo-Flite®dryer (Metso Minerals Industries Inc.; Danville; U.S.A.). Alternativelya fluidized bed may be used. In cases where the product needs to bedried with a predetermined and narrow residence time it is possible touse torus disc dryers or paddle dryers, for example a Nara paddle dryer(NARA Machinery Europe; Frechen; Germany), but designed for and operatedwith low pressure steam or heating liquid as the product temperatureduring drying does not need to exceed 160° C., preferably does not needto exceed 150° C., more preferably does not need to exceed 140° C., mostpreferably from 90 to 135° C.

In a preferred embodiment of the present invention, polyvalent cationscited in the postcrosslinking section are applied to the particlesurface before, during or after addition of the postcrosslinker by usingdifferent addition points along the axis of a horizontal mixer.

In a very particular preferred embodiment of the present invention thesteps of thermal posttreatment, postcrosslinking, and coating arecombined in one process step. Suitable coatings are cationic polymers,surfactants, and inorganic inert substances that are cited in thecoating section. The coating agent can be applied to the particlesurface before, during or after addition of the postcrosslinker also byusing different addition points along the axis of a horizontal mixer.

The polyvalent cations and/or the cationic polymers can act asadditional scavengers for residual postcrosslinkers. In a preferredembodiment of the present invention the postcrosslinkers are added priorto the polyvalent cations and/or the cationic polymers to allow thepostcrosslinker to react first.

The surfactants and/or the inorganic inert substances can be used toavoid sticking or caking during this process step under humidatmospheric conditions. A preferred surfactant is Span® 20. Preferredinorganic inert substances are precipitated silicas and fumed silcas inform of powder or dispersion.

The amount of total liquid used for preparing the solutions/dispersionsis typically from 0.01% to 25% by weight, preferably from 0.5% to 12% byweight, more preferably from 2% to 7% by weight, most preferably from 3%to 6% by weight, in respect to the weight amount of water-absorbentpolymer particles to be processed.

PREFERRED EMBODIMENTS ARE DEPICTED IN FIGS. 1 TO 8

FIG. 1: Process scheme (with external fluidized bed)

FIG. 2: Process scheme (without external fluidized bed)

FIG. 3: Arrangement of the T_outlet measurement

FIG. 4: Arrangement of the dropletizer units

FIG. 5: Dropletizer unit (longitudinal cut)

FIG. 6: Dropletizer unit (cross sectional view)

FIG. 7: Process scheme (external thermal posttreatment andpostcrosslinking)

FIG. 8: Process scheme (external thermal posttreatment, postcrosslinkingand coating)

The reference numerals have the following meanings:

-   1 Drying gas inlet pipe-   2 Drying gas amount measurement-   3 Gas distributor-   4 Dropletizer units-   5 Cocurrent spray dryer, cylindrical part-   6 Cone-   7 T_outlet measurement-   8 Tower offgas pipe-   9 Baghouse filter-   10 Ventilator-   11 Quench nozzles-   12 Condenser column, counter current cooling-   13 Heat exchanger-   14 Pump-   15 Pump-   16 Water outlet-   17 Ventilator-   18 Offgas outlet-   19 Nitrogen inlet-   20 Heat exchanger-   21 Ventilator-   22 Heat exchanger-   23 Steam injection via nozzles-   24 Water loading measurement-   25 Conditioned internal fluidized bed gas-   26 Internal fluidized bed product temperature measurement-   27 Internal fluidized bed-   28 Product discharge into external fluidized bed, rotary valve-   19 External fluidized bed-   30 Ventilator-   31 External fluidized bed offgas outlet to baghouse filter-   32 Rotary valve-   33 Sieve-   34 End product-   35 Filtered air inlet-   36 Ventilator-   37 Heat exchanger-   38 Steam injection via nozzles-   39 Water loading measurement-   40 Conditioned external fluidized bed gas-   41 Static mixer-   42 Static mixer-   43 Initiator feed-   44 Initiator feed-   45 Monomer feed-   46 Fine particle fraction outlet to rework-   47 T_outlet measurement (average temperature out of 3 measurements    around tower circumference)-   48 Dropletizer unit-   49 Monomer premixed with initiator feed-   50 Spray dryer tower wall-   51 Dropletizer unit outer pipe-   52 Dropletizer unit inner pipe-   53 Dropletizer cassette-   54 Teflon block-   55 Valve-   56 Monomer premixed with initiator feed inlet pipe connector-   57 Droplet plate-   58 Counter plate-   59 Flow channels for temperature control water-   60 Dead volume free flow channel for monomer solution-   61 Dropletizer cassette stainless steel block-   62 External thermal posttreatment-   63 Optional coating feed-   64 Postcrosslinker feed-   65 Thermal dryer (postcrosslinking)-   66 Cooler-   67 Optional coating/water feed-   68 Coater-   69 Coating/water feed

The drying gas is feed via a gas distributor (3) at the top of the spraydryer as shown in FIG. 1. The drying gas is partly recycled (drying gasloop) via a baghouse filter (9) and a condenser column (12). Thepressure inside the spray dryer is below ambient pressure.

The spray dryer outlet temperature is preferably measured at threepoints around the circumference at the end of the cylindrical part asshown in FIG. 3. The single measurements (47) are used to calculate theaverage cylindrical spray dryer outlet temperature.

The product accumulated in the internal fluidized bed (27). Conditionedinternal fluidized bed gas is fed to the internal fluidized bed (27) vialine (25). The relative humidity of the internal fluidized bed gas ispreferably controlled by adding steam via line (23).

The spray dryer offgas is filtered in baghouse filter (9) and sent to acondenser column (12) for quenching/cooling. After the baghouse filter(9) a recuperation heat exchanger system for preheating the gas afterthe condenser column (12) can be used. Excess water is pumped out of thecondenser column (12) by controlling the (constant) filling level insidethe condenser column (12). The water inside the condenser column (12) iscooled by a heat exchanger (13) and pumped counter-current to the gasvia quench nozzles (11) so that the temperature inside the condensercolumn (12) is preferably from 20 to 100° C., more preferably from 30 to80° C., most preferably from 40 to 75° C. The water inside the condensercolumn (12) is set to an alkaline pH by dosing a neutralizing agent towash out vapors of monomer a). Aqueous solution from the condensercolumn (12) can be sent back for preparation of the monomer solution.

The condenser column offgas is split to the drying gas inlet pipe (1)and the conditioned internal fluidized bed gas (25). The gastemperatures are controlled via heat exchangers (20) and (22). The hotdrying gas is fed to the cocurrent spray dryer via gas distributor (3).The gas distributor (3) consists preferably of a set of plates providinga pressure drop of preferably 1 to 100 mbar, more preferably 2 to 30mbar, most preferably 4 to 20 mbar, depending on the drying gas amount.Turbulences and/or a centrifugal velocity can also be introduced intothe drying gas if desired by using gas nozzles or baffle plates.

The product is discharged from the internal fluidized bed (27) viarotary valve (28) into external fluidized bed (29). Conditioned externalfluidized bed gas is fed to the external fluidized bed (29) via line(40). The relative humidity of the external fluidized bed gas ispreferably controlled by adding steam via line (38).The product holdupin the internal fluidized bed (27) can be controlled via weir height orrotational speed of the rotary valve (28).

The product is discharged from the external fluidized bed (29) viarotary valve (32) into sieve (33). The product holdup in the externalfluidized bed (28) can be controlled via weir height or rotational speedof the rotary valve (32). The sieve (33) is used for sieving offovers/lumps.

The monomer solution is preferably prepared by mixing first monomer a)with a neutralization agent and secondly with crosslinker b). Thetemperature during neutralization is controlled to preferably from 5 to60° C., more preferably from 8 to 40° C., most preferably from 10 to 30°C., by using a heat exchanger and pumping in a loop. A filter unit ispreferably used in the loop after the pump. The initiators are meteredinto the monomer solution upstream of the dropletizer by means of staticmixers (41) and (42) via lines (43) and (44) as shown in FIG. 1.Preferably a peroxide solution having a temperature of preferably from 5to 60° C., more preferably from 10 to 50° C., most preferably from 15 to40° C., is added via line (43) and preferably an azo initiator solutionhaving a temperature of preferably from 2 to 30° C., more preferablyfrom 3 to 15° C., most preferably from 4 to 8° C., is added via line(44). Each initiator is preferably pumped in a loop and dosed viacontrol valves to each dropletizer unit. A second filter unit ispreferably used after the static mixer (42). The mean residence time ofthe monomer solution admixed with the full initiator package in thepiping before the droplet plates (57) is preferably less than 60s, morepreferably less than 30 s, most preferably less than 10 s.

For dosing the monomer solution into the top of the spray dryerpreferably three dropletizer units are used as shown in FIG. 4.

A dropletizer unit consists of an outer pipe (51) having an opening forthe dropletizer cassette (53) as shown in FIG. 5. The dropletizercassette (53) is connected with an inner pipe (52). The inner pipe (53)having a PTFE block (54) at the end as sealing can be pushed in and outof the outer pipe (51) during operation of the process for maintenancepurposes.

The temperature of the dropletizer cassette (61) is controlled topreferably 5 to 80° C., more preferably 10 to 70° C., most preferably 30to 60° C., by water in flow channels (59) as shown in FIG. 6.

The dropletizer cassette has preferably from 10 to 1500, more preferablyfrom 50 to 1000, most preferably from 100 to 500, bores having adiameter of preferably from 50 to 500 μm, more preferably from 100 to300 μm, most preferably from 150 to 250 μm. The bores can be ofcircular, rectangular, triangular or any other shape. Circular bores arepreferred. The ratio of bore length to bore diameter is preferably from0.5 to 10, more preferably from 0.8 to 5, most preferably from 1 to 3.The droplet plate (57) can have a greater thickness than the bore lengthwhen using an inlet bore channel. The droplet plate (57) is preferablylong and narrow as disclosed in WO 2008/086976 A1. Multiple rows ofbores per droplet plate can be used, preferably from 1 to 20 rows, morepreferably from 2 to 5 rows.

The dropletizer cassette (61) consists of a flow channel (60) havingessential no stagnant volume for homogeneous distribution of thepremixed monomer and initiator solutions and two droplet plates (57).The droplet plates (57) have an angled configuration with an angle ofpreferably from 1 to 90°, more preferably from 3 to 45°, most preferablyfrom 5 to 20°. Each droplet plate (57) is preferably made of stainlesssteel or fluorous polymers, such as perfluoroalkoxyethylene,polytetrafluoroethylene, ethylene-chlorotrifluoroethylene copolymers,ethylene-tetrafluoroethylene copolymers and fluorinated polyethylene.Coated droplet plates as disclosed in WO 2007/031441 A1 can also beused. The choice of material for the droplet plate is not limited exceptthat droplet formation must work and it is preferable to use materialswhich do not catalyze the start of polymerization on its surface.

The throughput of monomer including initiator solutions per dropletizerunit is preferably from 150 to 2500 kg/h, more preferably from 200 to1000 kg/h, most preferably from 300 to 600 kg/h. The throughput per boreis preferably from 0.5 to 10 kg/h, more preferably from 0.8 to 5 kg/h,most preferably from 1 to 3 kg/h.

Water-Absorbent Polymer Particles

The water-absorbent polymer particles obtainable by dropletizationpolymerization have a mean sphericity of from 0.86 to 0.99, preferablyfrom 0.86 to 0.99, more preferably from 0.88 to 0.95, most preferablyfrom 0.89 to 0.93. The sphericity (SPHT) is defined as

${{SPHT} = \frac{4\pi \; A}{U^{2}}},$

where A is the cross-sectional area and U is the cross-sectionalcircumference of the polymer particles. The mean sphericity is thevolume-average sphericity.

The mean sphericity can be determined, for example, with the Camsizer®image analysis system (Retsch Technolgy GmbH; Haan; Germany):

For the measurement, the product is introduced through a funnel andconveyed to the falling shaft with a metering channel. While theparticles fall past a light wall, they are recorded selectively by acamera. The images recorded are evaluated by the software in accordancewith the parameters selected.

To characterize the roundness, the parameters designated as sphericityin the program are employed. The parameters reported are the meanvolume-weighted sphericities, the volume of the particles beingdetermined via the equivalent diameter xc_(min). To determine theequivalent diameter xc_(min), the longest chord diameter for a total of32 different spatial directions is measured in each case. The equivalentdiameter xc_(min) is the shortest of these 32 chord diameters. To recordthe particles, the so-called CCD-zoom camera (CAM-Z) is used. To controlthe metering channel, a surface coverage fraction in the detectionwindow of the camera (transmission) of 0.5% is predefined.

Water-absorbent polymer particles with relatively low sphericity areobtained by reverse suspension polymerization when the polymer beads areagglomerated during or after the polymerization.

The water-absorbent polymer particles prepared by customary solutionpolymerization (gel polymerization) are ground and classified afterdrying to obtain irregular polymer particles. The mean sphericity ofthese polymer particles is between approx. 0.72 and approx. 0.78.

The water-absorbent polymer particles obtainable by dropletizationpolymerization have a content of hydrophobic solvent of preferably lessthan 0.005% by weight, more preferably less than 0.002% by weight andmost preferably less than 0.001% by weight. The content of hydrophobicsolvent can be determined by gas chromatography, for example by means ofthe headspace technique.

Water-absorbent polymer particles which have been obtained by reversesuspension polymerization still comprise typically approx. 0.01% byweight of the hydrophobic solvent used as the reaction medium.

The water-absorbent polymer particles obtainable by dropletizationpolymerization have a dispersant content of typically less than 1% byweight, preferably less than 0.5% by weight, more preferably less than0.1% by weight and most preferably less than 0.05% by weight.

Water-absorbent polymer particles which have been obtained by reversesuspension polymerization still comprise typically at least 1% by weightof the dispersant, i.e. ethylcellulose, used to stabilize thesuspension.

The water-absorbent polymer particles obtainable by dropletizationpolymerization have a bulk density preferably at least 0.6 g/cm³, morepreferably at least 0.65 g/cm³, most preferably at least 0.7 g/cm³, andtypically less than 1 g/cm³.

The average particle diameter of the water-absorbent polymer particlesobtainable by dropletization polymerization is preferably from 250 to550 μm, more preferably from 350 to 500 μm, most preferably from 400 to450 μm.

The particle diameter distribution is preferably less than 0.7, morepreferably less than 0.65, more preferably less than 0.6.

Particle morphologies of the water-absorbent polymer particles areinvestigated in the swollen state by microscope analysis. Thewater-absorbent polymer particles can be divided into three categories:Type 1 are particles with one cavity having diameters typically from 0.4to 2.5 mm, Type 2 are particles with more than one cavity havingdiameters typically from 0.001 to 0.3 mm, and Type 3 are solid particleswith no visible cavity. Cavities with less than 1 μm diameter areconsidered as not visible cavities.

The ratio of particles having one cavity (Type 1) to particles havingmore than one cavity (Type 2) is preferably less than 1.0, morepreferably less than 0.7, most preferably less than 0.4. Lower ratioscorrelated with higher bulk densities.

The water-absorbent polymer particles obtainable by dropletizationpolymerization have a moisture content of preferably from 0.5 to 15% byweight, more preferably from 3 to 12% by weight, most preferably from 5to 10% by weight.

The water-absorbent polymer particles obtainable by dropletizationpolymerization have a centrifuge retention capacity (CRC) of typicallyat least 20 g/g, preferably at least 25 g/g, preferentially at least 28g/g, more preferably at least 30 g/g, most preferably at least 32 g/g.The centrifuge retention capacity (CRC) of the water-absorbent polymerparticles is typically less than 60 g/g.

The water-absorbent polymer particles obtainable by dropletizationpolymerization have an absorbency under a load of 49.2 g/cm² (AUHL) oftypically at least 15 g/g, preferably at least 16 g/g, preferentially atleast 20 g/g, more preferably at least 23 g/g, most preferably at least25 g/g, and typically not more than 50 g/g.

The water-absorbent polymer particles obtainable by dropletizationpolymerization have a saline flow conductivity (SFC) of typically atleast 10×10⁻⁷ cm³ s/g, usually at least 20×10⁻⁷ cm³ s/g, preferably atleast 50×10⁻⁷ cm³ s/g, preferentially at least 80×10⁻⁷ cm³ s/g, morepreferably at least 120×10⁻⁷ cm³ s/g, most preferably at least 150×10⁻⁷cm³ s/g, and typically not more than 300×10⁻⁷ cm³ s/g.

The water-absorbent polymer particles obtainable by dropletizationpolymerization have a free swell gel bed permeability (GBP) of typicallyat least 5 Darcies, usually at least 10 Darcies, preferably at least 20Darcies, preferentially at least 30 Darcies, more preferably at least 40Darcies, most preferably at least 50 Darcies, and typically not morethan 250 Darcies.

The water-absorbent polymer particles obtainable by dropletizationpolymerization can be mixed with other water-absorbent polymer particlesprepared by other processes, i.e. solution polymerization.

C. Fluid-Absorbent Articles

The fluid-absorbent article comprises of

(A) an upper liquid-pervious layer

(B) a lower liquid-impervious layer

(C) a fluid-absorbent core between (A) and (B) comprising an optionalcore cover, a fluid-storage layer comprising

at least 75% by weight water-absorbent polymer particles and anadhesive;

preferably at least 80% by weight water-absorbent polymer particles andan adhesive;

more preferably at least 83% by weight water-absorbent polymer particlesand an adhesive;

most preferably at least 85% by weight water-absorbent polymer particlesand an adhesive;

and an optional dusting layer

(D) an optional acquisition-distribution layer between (A) and (C),comprising

at least 80% by weight fibrous material and water-absorbent polymerparticles;

preferably at least 85% by weight fibrous material and water-absorbentpolymer particles;

more preferably at least 90% by weight fibrous material andwater-absorbent polymer particles;

most preferably at least 95% by weight fibrous material andwater-absorbent polymer particles;

(E) an optional tissue layer disposed immediately above and/or below(C); and

(F) other optional components.

Fluid-absorbent articles are understood to mean, for example,incontinence pads and incontinence briefs for adults or diapers forbabies. Suitable fluid-absorbent articles including fluid-absorbentcompositions comprising fibrous materials and optionally water-absorbentpolymer particles to form fibrous webs or matrices for the substrates,layers, sheets and/or the fluid-absorbent core.

Suitable fluid-absorbent articles are composed of several layers whoseindividual elements must show preferably definite functional parametersuch as dryness for the upper liquid-pervious layer, vapor permeabilitywithout wetting through for the lower liquid-impervious layer, aflexible, vapor permeable and thin fluid-absorbent core, showing fastabsorption rates and being able to retain highest quantities of bodyfluids, and an acquisition-distribution layer between the upper layerand the core, acting as transport and distribution layer of thedischarged body fluids. These individual elements are combined such thatthe resultant fluid-absorbent article meets overall criteria such asflexibility, water vapor breathability, dryness, wearing comfort andprotection on the one side, and concerning liquid retention, rewet andprevention of wet through on the other side. The specific combination ofthese layers provides a fluid-absorbent article delivering both highprotection levels as well as high comfort to the consumer.

Liquid-Pervious Layer (A)

The liquid-pervious layer (A) is the layer which is in direct contactwith the skin. Thus, the liquid-pervious layer is preferably compliant,soft feeling and non-irritating to the consumer's skin. Generally, theterm “liquid-pervious” is understood thus permitting liquids, i.e. bodyfluids such as urine, menses and/or vaginal fluids to readily penetratethrough its thickness. The principle function of the liquid-perviouslayer is the acquisition and transport of body fluids from the wearertowards the fluid-absorbent core. Typically liquid-pervious layers areformed from any materials known in the art such as nonwoven material,films or combinations thereof. Suitable liquid-pervious layers (A)consist of customary synthetic or semisynthetic fibers or bicomponentfibers or films of polyester, polyolefins, rayon or natural fibers orany combinations thereof. In the case of nonwoven materials, the fibersshould generally be bound by binders such as polyacrylates. Additionallythe liquid-pervious layer may contain elastic compositions thus showingelastic characteristics allowing to be stretched in one or twodirections.

Suitable synthetic fibers are made from polyvinyl chloride, polyvinylfluoride, polytetrafluorethylene, polyvinylidene chloride, polyacrylics,polyvinyl acetate, polyethylvinyl acetate, non-soluble or solublepolyvinyl alcohol, polyolefins such as polyethylene, polypropylene,polyamides, polyesters, polyurethanes, polystyrenes and the like.

Examples for films are apertured formed thermoplastic films, aperturedplastic films, hydroformed thermoplastic films, reticulatedthermoplastic films, porous foams, reticulated foams, and thermoplasticscrims.

Examples of suitable modified or unmodified natural fibers includecotton, bagasse, kemp, flax, silk, wool, wood pulp, chemically modifiedwood pulp, jute, rayon, ethyl cellulose, and cellulose acetate.

Suitable wood pulp fibers can be obtained by chemical processes such asthe Kraft and sulfite processes, as well as from mechanical processes,such as ground wood, refiner mechanical, thermo-mechanical,chemi-mechanical and chemi-thermo-mechanical pulp processes. Further,recycled wood pulp fibers, bleached, unbleached, elementally chlorinefree (ECF) or total chlorine free (TCF) wood pulp fibers can be used.

The fibrous material may comprise only natural fibers or syntheticfibers or any combination thereof. Preferred materials are polyester,rayon and blends thereof, polyethylene, and polypropylene.

The fibrous material as a component of the fluid-absorbent compositionsmay be hydrophilic, hydrophobic or can be a combination of bothhydrophilic and hydrophobic fibers. The definition of hydrophilic isgiven in the section “definitions” in the chapter above. The selectionof the ratio hydrophilic/hydrophobic and accordingly the amount ofhydrophilic and hydrophobic fibers within fluid-absorbent compositionwill depend upon fluid handling properties and the amount ofwater-absorbent polymer particles of the resulting fluid-absorbentcomposition. Such, the use of hydrophobic fibers is preferred if thefluid-absorbent composition is adjacent to the wearer of thefluid-absorbent article, that is to be used to replace partially orcompletely the upper liquid-pervious layer, preferably formed fromhydrophobic nonwoven materials. Hydrophobic fibers can also be member ofthe lower breathable, but fluid-impervious layer, acting there as afluid-impervious barrier.

Examples for hydrophilic fibers are cellulosic fibers, modifiedcellulosic fibers, rayon, polyester fibers such as polyethylenterephthalate, hydrophilic nylon and the like. Hydrophilic fibers canalso be obtained from hydrophobic fibers which are hydrophilized by e.g.surfactant-treating or silica-treating. Thus, hydrophilic thermoplasticfibers derived from polyolefins such as polypropylene, polyamides,polystyrenes or the like by surfactant-treating or silica-treating.

To increase the strength and the integrity of the upper-layer, thefibers should generally show bonding sites, which act as crosslinksbetween the fibers within the layer.

Technologies for consolidating fibers in a web are mechanical bonding,thermal bonding and chemical bonding. In the process of mechanicalbonding the fibers are entangled mechanically, e.g., by water jets(spunlace) to give integrity to the web. Thermal bonding is carried outby means of rising the temperature in the presence of low-meltingpolymers. Examples for thermal bonding processes are spunbonding,through-air bonding and resin bonding.

Preferred means of increasing the integrity are thermal bonding,spunbonding, resin bonding, through-air bonding and/or spunlace.

In the case of thermal bonding, thermoplastic material is added to thefibers. Upon thermal treatment at least a portion of this thermoplasticmaterial is melting and migrates to intersections of the fibers causedby capillary effects. These intersections solidify to bond sites aftercooling and increase the integrity of the fibrous matrix. Moreover, inthe case of chemically stiffened cellulosic fibers, melting andmigration of the thermoplastic material has the effect of increasing thepore size of the resultant fibrous layer while maintaining its densityand basis weight. Upon wetting, the structure and integrity of the layerremains stable. In summary, the addition of thermoplastic material leadsto improved fluid permeability of discharged body fluids and thus toimproved acquisition properties.

Suitable thermoplastic materials including polyolefins such aspolyethylene and polypropylene, polyesters, copolyesters, polyvinylacetate, polyethylvinyl acetate, polyvinyl chloride, polyvinylidenechloride, polyacrylics, polyamides, copolyamides, polystyrenes,polyurethanes and copolymers of any of the mentioned polymers.

Suitable thermoplastic fibers can be made from a single polymer that isa monocomponent fiber. Alternatively, they can be made from more thanone polymer, e.g., bi-component or multicomponent fibers. The term“bicomponent fibers” refers to thermoplastic fibers that comprise a corefiber made from a different fiber material than the shell. Typically,both fiber materials have different melting points, wherein generallythe sheath melts at lower temperatures. Bi-component fibers can beconcentric or eccentric depending whether the sheath has a thicknessthat is even or uneven through the cross-sectional area of thebi-component fiber. Advantage is given for eccentric bi-component fibersshowing a higher compressive strength at lower fiber thickness. Furtherbi-component fibers can show the feature “uncrimped” (unbent) or“crimped” (bent), further bi-component fibers can demonstrate differingaspects of surface lubricity.

Examples of bi-component fibers include the following polymercombinations: polyethylene/polypropylene, polyethylvinylacetate/polypropylene, polyethylene/polyester, polypropylene/polyester,copolyester/polyester and the like.

Suitable thermoplastic materials have a melting point of lowertemperatures that will damage the fibers of the layer; but not lowerthan temperatures, where usually the fluid-absorbent articles arestored. Preferably the melting point is between about 75° C. and 175° C.The typical length of thermoplastic fibers is from about 0.4 to 6 cm,preferably from about 0.5 to 1 cm. The diameter of thermoplastic fibersis defined in terms of either denier (grams per 9000 meters) or dtex(grams per 10 000 meters). Typical thermoplastic fibers have a dtex inthe range from about 1.2 to 20, preferably from about 1.4 to 10.

A further mean of increasing the integrity of the fluid-absorbentcomposition is the spunbonding technology. The nature of the productionof fibrous layers by means of spunbonding is based on the directspinning of polymeric granulates into continuous filaments andsubsequently manufacturing the fibrous layer.

Spunbond fabrics are produced by depositing extruded, spun fibers onto amoving belt in a uniform random manner followed by thermal bonding thefibers. The fibers are separated during the web laying process by airjets. Fiber bonds are generated by applying heated rolls or hot needlesto partially melt the polymer and fuse the fibers together. Sincemolecular orientation increases the melting point, fibers that are nothighly drawn can be used as thermal binding fibers. Polyethylene orrandom ethylene/propylene copolymers are used as low melting bondingsites.

Besides spunbonding, the technology of resin bonding also belongs tothermal bonding subjects. Using this technology to generate bondingsites, specific adhesives, based on e.g. epoxy, polyurethane and acrylicare added to the fibrous material and the resulting matrix is thermaltreated. Thus the web is bonded with resin and/or thermal plastic resinsdispersed within the fibrous material.

As a further thermal bonding technology through-air bonding involves theapplication of hot air to the surface of the fibrous fabric. The hot airis circulated just above the fibrous fabric, but does not push throughthe fibrous fabric. Bonding sites are generated by the addition ofbinders. Suitable binders used in through-air thermal bonding includecrystalline binder fibers, bi-component binder fibers, and powders. Whenusing crystalline binder fibers or powders, the binder melts entirelyand forms molten droplets throughout the nonwoven's cross-section.Bonding occurs at these points upon cooling. In the case of sheath/corebinder fibers, the sheath is the binder and the core is the carrierfiber. Products manufactured using through-air ovens tend to be bulky,open, soft, strong, extensible, breathable and absorbent. Through-airbonding followed by immediate cold calendering results in a thicknessbetween a hot roll calendered product and one that has been though-airbonded without compression. Even after cold calendering, this product issofter, more flexible and more extensible than area-bond hot-calenderedmaterial.

Spunlacing (“hydroentanglement”) is a further method of increasing theintegrity of a web. The formed web of loose fibers (usually air-laid orwet-laid) is first compacted and prewetted to eliminate air pockets. Thetechnology of spunlacing uses multiple rows of fine high-speed jets ofwater to strike the web on a porous belt or moving perforated orpatterned screen so that the fibers knot about one another. The waterpressure generally increases from the first to the last injectors.Pressures as high as 150 bar are used to direct the water jets onto theweb. This pressure is sufficient for most of the nonwoven fibers,although higher pressures are used in specialized applications.

The spunlace process is a nonwovens manufacturing system that employsjets of water to entangle fibers and thereby provide fabric integrity.Softness, drape, conformability, and relatively high strength are themajor characteristics of spunlace nonwoven.

In newest researches benefits are found in some structural features ofthe resulting liquid-pervious layers. For example, the thickness of thelayer is very important and influences together with its x-y dimensionthe acquisition-distribution behavior of the layer. If there is furthersome profiled structure integrated, the acquisition-distributionbehavior can be directed depending on the three-dimensional structure ofthe layer. Thus 3D-polyethylene in the function of liquid-pervious layeris preferred.

Thus, suitable liquid-pervious layers (A) are nonwoven layers formedfrom the fibers above by thermal bonding, spunbonding, resin bonding orthrough-air bonding. Further suitable liquid-pervious layers are3D-polyethylene layers and spunlace.

Preferably the 3D-polyethylene layers and spunlace show basis weightsfrom 12 to 22 gsm.

Typically liquid-pervious layers (A) extend partially or wholly acrossthe fluid-absorbent structure and can extend into and/or form part ofall the preferred sideflaps, side wrapping elements, wings and ears.

Liquid-Impervious Layer (B)

The liquid-impervious layer (B) prevents the exudates absorbed andretained by the fluid-absorbent core from wetting articles which are incontact with the fluid-absorbent article, as for example bedsheets,pants, pyjamas and undergarments. The liquid-impervious layer (B) maythus comprise a woven or a nonwoven material, polymeric films such asthermoplastic film of polyethylene or polypropylene, or compositematerials such as film-coated nonwoven material.

Suitable liquid-impervious layers include nonwoven, plastics and/orlaminates of plastic and nonwoven. Both, the plastics and/or laminatesof plastic and nonwoven may appropriately be breathable, that is, theliquid-impervious layer (B) can permit vapors to escape from thefluid-absorbent material. Thus the liquid-impervious layer has to have adefinite water vapor transmission rate and at the same time the level ofimpermeability. To combine these features, suitable liquid-imperviouslayers including at least two layers, e.g. laminates from fibrousnonwoven having a specified basis weight and pore size, and a continuousthree-dimensional film of e.g. polyvinylalcohol as the second layerhaving a specified thickness and optionally having pore structure. Suchlaminates acting as a barrier and showing no liquid transport or wetthrough. Thus, suitable liquid-impervious layers comprising at least afirst breathable layer of a porous web which is a fibrous nonwoven, e.g.a composite web of a meltblown nonwoven layer or of a spunbondednonwoven layer made from synthetic fibers and at least a second layer ofa resilient three dimensional web consisting of a liquid-imperviouspolymeric film, e.g. plastics optionally having pores acting ascapillaries, which are preferably not perpendicular to the plane of thefilm but are disposed at an angle of less than 90° relative to the planeof the film.

Suitable liquid-impervious layers are permeable for vapor. Preferablythe liquid-impervious layer is constructed from vapor permeable materialshowing a water vapor transmission rate (WVTR) of at least about 100 gsmper 24 hours, preferably at least about 250 gsm per 24 hours and mostpreferred at least about 500 gsm per 24 hours.

Preferably the liquid-impervious layer (B) is made of nonwovencomprising hydrophobic materials, e.g. synthetic fibers or aliquid-impervious polymeric film comprising plastics e.g. polyethylene.The thickness of the liquid-impervious layer is preferably 15 to 30 μm.

Further, the liquid-impervious layer (B) is preferably made of alaminate of nonwoven and plastics comprising a nonwoven having a densityof 12 to 15 gsm and a polyethylene layer having a thickness of about 10to 20 μm.

The typically liquid-impervious layer (B) extends partially or whollyacross the fluid-absorbent structure and can extend into and/or formpart of all the preferred sideflaps, side wrapping elements, wings andears.

Fluid-Absorbent Core (C)

The fluid-absorbent core (C) is disposed between the upperliquid-pervious layer (A) and the lower liquid-impervious layer (B).Suitable fluid-absorbent cores (C) may be selected from any of thefluid-absorbent core-systems known in the art provided that requirementssuch as vapor peimeability, flexibility and thickness are met. Suitablefluid-absorbent cores refer to any fluid-absorbent composition whoseprimary function is to acquire, transport, distribute, absorb, store andretain discharged body fluids.

The top view area of the fluid-absorbent core (C) is preferably at least200 cm², more preferably at least 250 cm², most preferably at least 300cm². The top view area is the part of the core that is face-to-face tothe upper liquid-pervious layer.

The fluid-absorbent core comprises a substrate layer, i.e. a nonwovenlayer or a tissue paper, water-absorbent polymer particles, and anadhesive.

Suitable nonwoven layers for the present invention include those madeusing synthetic polymeric fibers. The synthetic polymeric fibers may beformed from any polymeric material capable of forming fibers whichfibers can be formed into a nonwoven layer. Suitable polymeric materialfrom which the synthetic polymeric fibers may be formed includepolyolefins, such as polyethylene, polypropylene, and the like,polyesters such as polyethylene terephthalate and the like, polyamidessuch as nylon 6, nylon 6,6, poly (iminocarboxylpentamethylene) and thelike, acrylics, and modified cellulosic material, such as celluloseacetate and rayon; as well as mixtures and copolymers thereof.

The synthetic polymeric fibers may be formed by meltblowing, through aspunbond process, by extrusion and drawing, or other wet, dry and meltspinning methods known to those skilled in the art. The syntheticpolymeric fibers from which the nonwoven layer is formed may have adiscrete length or may be substantially continuous. For example, if thesynthetic polymeric fibers are formed by meltblowing, the fibers may besubstantially continuous (few visible ends). If the fibers are formed byextrusion and drawing to produce a tow, the tow may be used as producedor cut into staple fibers having a length, for example, of from about 25to 75 mm or short cut into lengths of from about 1 to 25 mm. Thesynthetic polymeric fibers may suitably have a maximum cross-sectionaldimension of from about 0.5 to 50 μm as determined by microscopicmeasurement using an optical microscope and a calibrated stagemicrometer or by measurement from Scanning Electron photomicrographs.

The nonwoven layers may be formed directly through a spunbond ormeltblown process, or by carding or air-laying staple or short cutfibers. Other methods of forming nonwoven layers known to those skilledin the art may be suited for use in the present invention. The nonwovenlayer may subsequently be bonded to enhance structural integrity.Methods of bonding nonwoven layers are known to those skilled in the artand include thermal bonding, point bonding, powder bonding, ultrasonicbonding, chemical bonding, mechanical entanglement, and the like. Thefibers may be homogenous fibers or may be a core/sheath or side-by-sidefibers known to those skilled in the art as bicomponent fibers.

The nonwoven layer may be formed from a single type of syntheticpolymeric fiber or may contain synthetic polymeric fibers formed fromdifferent polymeric materials, having different fiber lengths or maximumcross-sectional dimensions. For example, the nonwoven layer may comprisea mixture of (1) bicomponent fibers having a polyethylene sheath and apolypropylene core which bicomponent fibers have a maximumcross-sectional dimension of about 20 μm and a length of about 38 mm and(2) polyester fibers, i.e. polyethylene terephthalate, having a maximumcross-sectional dimension of about 25 μm and a length of about 38 mm.Fibers 1 and 2 may be combined in a weight ratio of from 1:99 to 99:1.The fibers may be uniformly mixed or may be concentrated at oppositeplanar surfaces of the nonwoven layer.

The nonwoven layer suitably comprises preferably from about 20 to 100%by weight, more preferably from about 25 to 100% by weight, mostpreferably from about 50 to 100% by weight, synthetic polymeric fibers.In addition to the synthetic polymeric fibers, the nonwoven layer maycontain from about 90 to 0% by weight of a non-synthetic polymeric fibersuch as wood pulp fluff cotton linters, cotton, and the like.

In one preferred embodiment, the nonwoven layer contains syntheticpolymeric fibers which are formed from a polymeric material having ahigh wet modulus. The importance of the modulus of a material isdiscussed in the monograph “Absorbency”, P. K. Chatterjee, Elsevier,1985. A polymeric material will be considered to have a high wet moduluswhen it has a wet modulus greater than about 80% of its dry modulus asdetermined by the ASTM test method D 2101-91 using modified gaugelengths. It is often desired to form the synthetic polymeric fibers ofthe nonwoven layer from a polymeric material having a high wet modulusbecause such materials generally form nonwoven layers which possess arelatively high degree of wet resiliency. The wet resilience of anonwoven layer is related to the pore structure (while under a load) ofthe nonwoven layer. As will be discussed in greater detail below, it isoften desired that the nonwoven layer have a relatively high degree ofwet resilience.

The pore structure (while under a load) of a fibrous structure formedfrom fibers of a polymeric material will, as discussed above, relate tothe wet and/or dry modulus of the constituent fibers. Wet modulus of theconstituent fibers should be considered for fibers that may likely bewetted during use. For the purposes of estimating the effect of load onthe pore structure of a fibrous structure formed from fibers of apolymeric material the tensile modulus of the fiber which can be relatedto the flexural rigidity of the fiber as shown in the monograph“Physical Properties of Textile Fibers”, W. E. Morton and J. W. S.Hearl, The Textile Institute, 1975, can be used.

As a general rule, the polymeric materials from which the syntheticpolymeric fibers of the nonwoven layer are formed will be inherentlyhydrophobic. As used herein, a polymeric material will be considered tobe “inherently” hydrophobic or hydrophilic when the polymeric material,free from any surface modifications or treatments, e.g., surface activeagents, spin finishes, blooming agents, etc., is hydrophobic orhydrophilic, respectively.

When the synthetic polymeric fibers of the nonwoven layer are formedfrom a polymeric material which is inherently hydrophobic, it is oftendesirable to treat the fibers with a surface modifying material torender the surface of the fiber hydrophilic. For example, a surfactantmay be applied to the fibers.

The nonwoven layer may also comprise hydrophilic fibers. The hydrophilicmaterials may be inherently hydrophilic such as cellulosic fibers suchas wood pulp fluff, cotton linters, and the like, regenerated cellulosefibers such as rayon, or certain nylon copolymers such as poly(pentamethylenecarbonamide) (nylon-6)/polyethylene oxide. Alternatively,the hydrophilic fibers may be hydrophobic fibers which have been treatedto possess a hydrophilic surface. For example, the fibers may be formedfrom a polyolefin material which is subsequently coated with a surfaceactive agent such that the fiber itself is hydrophilic as describedherein. Other methods of hydrophilizing fibers formed from hydrophobicmaterials are known and suited for use in the present invention.

Methods of providing inherently hydrophilic fibers such as wood pulpfluff are known. Hydrophobic fibers which can be treated to possess ahydrophilic surface are suitably formed by processes known to thoseskilled in the art. If the hydrophilic fibers are hydrophobic fiberswhich have been treated to possess a hydrophilic surface, the fiberswill suitably have a fiber length and maximum cross-sectional dimensionas set forth above. If the hydrophilic fibers are inherently hydrophilicsuch as wood pulp fluff, rayon, cotton, cotton linters and the like, thefibers will generally have a length of from about 1.0 to 50 mm and amaximum cross-sectional dimension of from about 0.5 to 100 μm.

The nonwoven layer suitably comprises preferably from about 10 to 100%by weight, more preferably from about 30 to 100% by weight, mostpreferably from about 55 to 100% by weight of hydrophilic fibers,preferably inherently hydrophilic fibers. In addition to the hydrophilicfibers, the nonwoven layer may contain from about 90 to 0% by weight ofa high wet modulus, preferably inherently hydrophobic, fibers. Thenonwoven layer may be formed from a single type of hydrophilic fiber ormay contain hydrophilic fibers having different compositions, lengthsand maximum cross-sectional dimensions.

In one preferred embodiment, the nonwoven layer is formed from air laidcellulosic fibers such as wood pulp fluff Wood pulp fluff fibers arepreferred for use due to their ready availability and due to the factthat the fibers are relatively inexpensive compared to syntheticpolymeric fibers.

The nonwoven layer suitably has a basis weight of preferably from about10 to 200 gsm, more preferably from about 20 to 150 gsm, most preferablyfrom about 25 to 125 gsm.

The nonwoven layer suitably has a density of preferably from about 0.04to 0.20 g/cm³, more preferably from about 0.06 to 0.16 g/cm³, mostpreferably from about 0.08 to 0.14 g/cm³.

Typically the fluid-absorbent cores may contain a single type ofwater-absorbent polymer particles or may contain water-absorbent polymerparticles derived from different kinds of water-absorbent polymermaterial. Thus, it is possible to add water-absorbent polymer particlesfrom a single kind of polymer material or a mixture of water-absorbentpolymer particles from different kinds of polymer materials, e.g. amixture of regular water-absorbent polymer particles, derived from gelpolymerization with water-absorbent polymer particles, derived fromdropletization polymerization. Alternatively it is possible to addwater-absorbent polymer particles derived from inverse suspensionpolymerization.

Alternatively it is possible to mix water-absorbent polymer particlesshowing different feature profiles. Thus, the fluid-absorbent core maycontain water-absorbent polymer particles with uniform pH value, or itmay contain water-absorbent polymer particles with different pH values,e.g. two- or more component mixtures from water-absorbent polymerparticles with a pH in the range from about 4.0 to about 7.0.Preferably, applied mixtures deriving from mixtures of water-absorbentpolymer particles got from gel polymerization or inverse suspensionpolymerization with a pH in the range from about 4.0 to about 7.0 andwater-absorbent polymer particles got from dropletizationpolymerization.

The fluid-absorbent core comprises at least 75% by weight, preferably atleast 80% by weight, more preferably at least 83% by weight, mostpreferably at least 85% by weight, of water-absorbent polymer particles.

The quantity of water-absorbent polymer particles within thefluid-absorbent core is preferably from 3 to 20 g, more preferably from6 to 14 g, most preferably from 8 to 12 g in the case of maxi-diapers,and in the case of incontinence products up to about 50 g.

The types of adhesives are not particularly limited. A wide variety ofthermoplastic compositions are suitable for use as pressure sensitiveadhesives in the present invention.

Thermoplastic compositions may comprise a single type of thermoplasticpolymers or a blend of thermoplastic polymers. Alternatively, thethermoplastic composition may comprise hot melt adhesives comprising atleast one thermoplastic polymer together with thermoplastic diluentssuch as tackifiers, plasticizers or other additives, e.g. antioxidants.The thermoplastic composition may further comprise pressure sensitivehot melt adhesives comprising e.g. crystalline polypropylene and anamorphous polyalphaolefine or styrene block copolymer and mixture ofwaxes.

Suitable thermoplastic polymers are styrenic block copolymers includingA-B-A triblock segments, A-B diblock segments and (A-B)_(n) radial blockcopolymer segments. The letter A designs non-elastomeric polymersegments, e.g. polystyrene, and B stands for unsaturated conjugateddiene or their (partly) hydrogenated form. Preferably B comprisesisoprene, butadiene, ethylene/butylene (hydrogenated butadiene),ethylene/propylene (hydrogenated isoprene) and mixtures thereof.

Other suitable thermoplastic polymers are amorphous polyolefins,amorphous polyalphaolefins and metallocene polyolefins.

The construction of the fluid-absorbent cores is made and controlled bythe discrete application of adhesives as known to people skilled in theart. Examples would be e.g. Dispomelt 505B, Dispomelt Cool 1101, as wellas other specific function adhesives manufactured by National Starch orHenkel.

Ultrathin fluid-absorbent cores are be formed by immobilization ofwater-absorbent polymer particles on a substrate layer using adhesives.Preferably the water-absorbent polymer particles form longitudinalstrips or discrete spots. Other patterns of the water-absorbent polymerparticles are also possible.

Typically, the water-absorbent polymer particles form a discontinuouslayer on the substrate layer, i.e. a nonwoven layer, covered by athermoplastic composition as adhesive forming discrete cavities, so thatthe water-absorbent polymer particles are immobilized.

It is also possible to use a second substrate layer that comprises anadhesive instead of the thermoplastic composition.

In a preferred embodiment the ultrathin fluid-absorbent cores compriseat least two layers of immobilized water-absorbent polymer particles.

Suitable fluid-absorbent cores may also include layers, which are formedby the process of manufacturing the fluid-absorbent article. The layeredstructure may be formed by subsequently generating the different layersin z-direction.

Alternatively a core-structure can be formed from two or more preformedlayers to get a layered fluid-absorbent core. These uniform or differentlayers can be fixed to each other at their adjacent plane surfaces.Alternatively, the layers may be combined in a way that a plurality ofchambers is formed, in which separately water-absorbent polymer materialis incorporated.

Further a composite structure can be formed from a carrier layer (e.g. apolymer film), onto which the water-absorbent polymer material isaffixed. The fixation can be done at one side or at both sides. Thecarrier layer may be pervious or impervious for body-fluids.

Typically fluid-absorbent articles comprising at least an upperliquid-pervious layer (A), at least a lower liquid-impervious layer (B)and at least one fluid-absorbent core between the layer (A) and thelayer (B) besides other optional layers. The addition of a secondfluid-absorbent core to the first fluid-absorbent core offers morepossibilities in body fluid transfer and distribution. Moreover higherquantities of discharged body fluids can be retained. Having theopportunity of combining several layers showing differentwater-absorbent polymer concentration and content, it is possible toreduce the thickness of the fluid-absorbent article to a minimum even ifthere are several fluid-absorbent cores included.

Suitable fluid-absorbent articles are including single or multi-coresystems in any combination with other layers which are typically foundin fluid-absorbent articles. Preferred fluid-absorbent articles includesingle- or double-core systems; most preferably fluid-absorbent articlesinclude a single fluid-absorbent core.

The fluid-absorbent core typically has a uniform size or profile.Suitable fluid-absorbent cores can also have profiled structures,concerning the shape of the core and/or the content of water-absorbentpolymer particles and/or the distribution of the water-absorbent polymerparticles and/or the dimensions of the different layers if a layeredfluid-absorbent core is present.

These layers or foldings are preferably joined to each e.g. by additionof adhesives or by mechanical, thermal or ultrasonic bonding orcombinations thereof. Water-absorbent polymer particles may be comprisedwithin or between the individual layers, e.g. by forming separatewater-absorbent polymer-layers.

The fluid-absorbent core may comprise additional additives typicallypresent in fluid-absorbent articles known in the art. Exemplaryadditives are odor control additives and wetness indication additives.

Concerning odor control, perfumes and/or odor control additives areoptionally added. Suitable odor control additives are all substances ofreducing odor developed in carrying fluid-absorbent articles over timeknown in the art. Thus, suitable odor control additives are inorganicmaterials, such as zeolites, activated carbon, bentonite, silica,aerosile, kieselguhr, clay; chelants such as ethylenediamine tetraaceticacid (EDTA), cyclodextrins, aminopolycarbonic acids, ethylenediaminetetramethylene phosphonic acid, aminophosphate, polyfunctional aromates,N,N-disuccinic acid.

Suitable odor control additives are further antimicrobial agents such asquaternary ammonium, phenolic, amide and nitro compounds and mixturesthereof; bactericides such as silver salts, zinc salts, cetylpyridiniumchloride and/or triclosan as well as surfactants having an HLB value ofless than 12.

Suitable odor control additives are further compounds with anhydridegroups such as maleic-, itaconic-, polymaleic- or polyitaconicanhydride, copolymers of maleic acid with C2-C8 olefins or styrene,polymaleic anhydride or copolymers of maleic anhydride with isobutene,di-isobutene or styrene, compounds with acid groups such as ascorbic,benzoic, citric, salicylic or sorbic acid and fluid-soluble polymers ofmonomers with acid groups, homo- or co-polymers of C3-05mono-unsaturated carboxylic acids.

Suitable odor control additives are further perfumes such as allylcaproate, allyl cyclohexaneacetate, allyl cyclohexanepropionate, allylheptanoate, amyl acetate, amyl propionate, anethol, anixic aldehyde,anisole, benzaldehyde, benzyl acetete, benzyl acetone, benzyl alcohole,benzyl butyrate, benzyl formate, camphene, camphor gum, laevo-carveol,cinnamyl formate, cis-jasmone, citral, citronellol and its derivatives,cuminic alcohol and its derivatives, cyclal C, dimethyl benzyl carbinoland its derivatives, dimethyl octanol and its derivatives, eucalyptol,geranyl derivatives, lavandulyl acetete, ligustral, d-limonene,linalool, linalyl derivatives, menthone and its derivatives, myrcene andits derivatives, neral, nerol, p-cresol, p-cymene, orange terpenes,alpha-ponene, 4-terpineol, thymol etc.

Masking agents are also used as odor control additives. Masking agentsare in solid wall material encapsulated perfumes. Preferably, the wallmaterial comprises a fluid-soluble cellular matrix which is used fortime-delay release of the perfume ingredient.

Further suitable odor control additives are transition metals such asCu, Ag, and Zn, enzymes such as urease-inhibitors, starch, pH bufferingmaterial, chitin, green tea plant extracts, ion exchange resin,carbonate, bicarbonate, phosphate, sulfate or mixtures thereof.

Preferred odor control additives are green tea plant extracts, silica,zeolite, carbon, starch, chelating agent, pH buffering material, chitin,kieselguhr, clay, ion exchange resin, carbonate, bicarbonate, phosphate,sulfate, masking agent or mixtures thereof. Suitable concentrations ofodor control additives are from about 0.5 to about 300 gsm.

Newest developments propose the addition of wetness indicationadditives. Besides electrical monitoring the wetness in thefluid-absorbent article, wetness indication additives comprising a hotmelt adhesive with a wetness indicator are known. The wetness indicationadditive changes the colour from yellow to a relatively dark and deepblue. This colour change is readily perceivable through theliquid-impervious outer material of the fluid-absorbent article.Existing wetness indication is also achieved via application of watersoluble ink patterned on the backsheet which disappears when wet.

Suitable wetness indication additives comprising a mixture of sorbitanmonooleate and polyethoxylated hydrogenated castor oil. Preferably, theamount of the wetness indication additive is in the range of about 1 to5% by weight related to the weight of the fluid-absorbent core.

The basis weight of the fluid-absorbent core is preferably in the rangeof 400 to 1200 gsm. The density of the fluid-absorbent core ispreferably in the range of 0.1 to 0.50 g/cm3. The thickness of thefluid-absorbent core is in the case of diapers preferably in the rangeof 1 to 5 mm, in the case of incontinence products preferably in therange of 3 to 15 mm.

Optional Acquisition-distribution Layer (D)

An optional acquisition-distribution layer (D) is located between theupper layer (A) and the fluid-absorbent core (C) and is preferablyconstructed to efficiently acquire discharged body fluids and totransfer and distribute them to other regions of the fluid-absorbentcomposition or to other layers, where the body fluids are immobilizedand stored. Thus, the upper layer transfers the discharged liquid to theacquisition-distribution layer (D) for distributing it to thefluid-absorbent core.

The acquisition-distribution layer comprises fibrous material andoptionally water-absorbent polymer particles.

The fibrous material may be hydrophilic, hydrophobic or can be acombination of both hydrophilic and hydrophobic fibers. It may bederived from natural fibers, synthetic fibers or a combination of both.

Suitable acquisition-distribution layers are formed from cellulosicfibers and/or modified cellulosic fibers and/or synthetics orcombinations thereof Thus, suitable acquisition-distribution layers maycontain cellulosic fibers, in particular wood pulp fluff Examples offurther suitable hydrophilic, hydrophobic fibers, as well as modified orunmodified natural fibers are given in the chapter “Liquid-perviousLayer (A)” above.

Especially for providing both fluid acquisition and distributionproperties, the use of modified cellulosic fibers is preferred. Examplesfor modified cellulosic fibers are chemically treated cellulosic fibers,especially chemically stiffened cellulosic fibers. The term “chemicallystiffened cellulosic fibers” means cellulosic fibers that have beenstiffened by chemical means to increase the stiffness of the fibers.Such means include the addition of chemical stiffening agent in the formof coatings and impregnates. Suitable polymeric stiffening agents caninclude: cationic modified starches having nitrogen-containing groups,latexes, wet strength resins such as polyamide-epichlorohydrin resin,polyacrylamide, urea formaldehyde and melamine formaldehyde resins andpolyethylenimine resins.

Stiffening may also include altering the chemical structure, e.g. bycrosslinking polymer chains. Thus crosslinking agents can be applied tothe fibers that are caused to chemically form intrafiber crosslinkbonds. Further cellulosic fibers may be stiffened by cross-link bonds inindividualized form. Suitable chemical stiffening agents are typicallymonomeric crosslinking agents including C₂-C₈ dialdehyde, C₂-C₈monoaldehyde having an acid functionality, and especially C₂-C₉polycarboxylic acids.

Preferably the modified cellulosic fibers are chemically treatedcellulosic fibers. Especially preferred are curly fibers which can beobtained by treating cellulosic fibers with citric acid. Preferably thebasis weight of cellulosic fibers and modified cellulosic fibers is from50 to 200 gsm.

Suitable acquisition-distribution layers further include syntheticfibers. Known examples of synthetic fibers are found in the Chapter“Liquid-pervious Layer (A)” above. 3D-poly-ethylene in the function ofacquisition-distribution layer is preferred.

Further, as in the case of cellulosic fibers, hydrophilic syntheticfibers are preferred. Hydrophilic synthetic fibers may be obtained bychemical modification of hydrophobic fibers. Preferably,hydrophilization is carried out by surfactant treatment of hydrophobicfibers. Thus the surface of the hydrophobic fiber can be renderedhydrophilic by treatment with a nonionic or ionic surfactant, e.g., byspraying the fiber with a surfactant or by dipping the fiber into asurfactant. Further preferred are permanent hydrophilic syntheticfibers.

The fibrous material of the acquisition-distribution layer may be fixedto increase the strength and the integrity of the layer. Technologiesfor consolidating fibers in a web are mechanical bonding, thermalbonding and chemical bonding. Detailed description of the differentmethods of increasing the integrity of the web is given in the Chapter“Liquid-pervious Layer (A)” above.

Preferred acquisition-distribution layers comprise fibrous material andwater-absorbent polymer particles distributed within. Thewater-absorbent polymer particles may be added during the process offorming the layer from loose fibers, or, alternatively, it is possibleto add monomer solution after the formation of the layer and polymerizethe coating solution by means of UV-induced polymerization technologies.Thus, “in situ”-polymerization is a further method for the applicationof water-absorbent polymers.

Thus, suitable acquisition-distribution layers comprising from 80 to100% by weight fibrous material and from 0 to 20% by weightwater-absorbent polymer particles; preferably from 85 to 99.9% by weightfibrous material and from 0.1 to 15% by weight water-absorbent polymerparticles; more preferably from 90 to 99.5% by weight fibrous materialand from 0.5 to 10% by weight water-absorbent polymer particles; andmost preferably from 95 to 99% by weight fibrous material and from 1 to5% by weight water-absorbent polymer particles.

Preferred acquisition-distribution layers show basis weights in therange from 20 to 200 gsm, most preferred in the range from 40 to 50 gsm,depending on the concentration of water-absorbent polymer particles.

Optional Tissue Layer (E)

An optional tissue layer is disposed immediately above and/or below (C).

The material of the tissue layer may comprise any known type ofsubstrate, including webs, garments, textiles and films. The tissuelayer may comprise natural fibers, such as cellulose, cotton, flax,linen, hemp, wool, silk, fur, hair and naturally occurring mineralfibers. The tissue layer may also comprise synthetic fibers such asrayon and lyocell (derived from cellulose), polysaccharides (starch),polyolefin fibers (polypropylene, polyethylene), polyamides, polyester,butadiene-styrene block copolymers, polyurethane and combinationsthereof Preferably, the tissue layer comprises cellulose fibers.

Other Optional Components (F) 1. Leg Cuff

Typical leg cuffs comprising nonwoven materials which can be formed bydirect extrusion processes during which the fibers and the nonwovenmaterials are formed at the same time, or by laying processes ofpreformed fibers which can be laid into nonwoven materials at a laterpoint of time. Examples for direct extrusion processes includespunbonding, meltblowing, solvent spinning, electrospinning andcombinations thereof. Examples of laying processes include wet-layingand dry-laying (e.g. air-laying, carding) methods. Combinations of theprocesses above include spunbond-meltblown-spunbond (sms),spunbond-meltblow-meltblown-spunbond (smms), spunbond-carded (sc),spunbond-airlaid (sa), meltblown-airlaid (ma) and combinations thereof.The combinations including direct extrusion can be combined at the samepoint in time or at a subsequent point in time. In the examples above,one or more individual layers can be produced by each process. Thus,“sms” means a three layer nonwoven material, “smsms” or “ssmms” means afive layer nonwoven material. Usually, small type letters (sms)designate individual layers, whereas capital letters (SMS) designate thecompilation of similar adjacent layers.

Further, suitable leg cuffs are provided with elastic strands.

Preferred are leg cuffs from synthetic fibers showing the layercombinations sms, smms or smsms. Preferred are nonwovens with thedensity of 13 to 17 gsm. Preferably leg cuffs are provided with twoelastic strands.

2. Elastics

The elastics are used for securely holding and flexibly closing thefluid-absorbent article around the wearer's body, e.g. the waist and thelegs to improve containment and fit. Leg elastics are placed between theouter and inner layers or the fluid-absorbent article, or between theouter cover and the bodyside liner. Suitable elastics comprising sheets,ribbons or strands of thermoplastic polyurethane, elastomeric materials,poly(ether-amide) block copolymers, thermoplastic rubbers,styrene-butadiene copolymers, silicon rubbers, natural rubbers,synthetic rubbers, styrene isoprene copolymers, styrene ethylenebutylene copolymers, nylon copolymers, spandex fibers comprisingsegmented polyurethane and/or ethylene-vinyl acetate copolymer. Theelastics may be secured to a substrate after being stretched, or securedto a stretched substrate. Otherwise, the elastics may be secured to asubstrate and then elastisized or shrunk, e.g. by the application ofheat.

3. Closing System

The closing system includes tape tabs, landing zone, elastomerics, pullups and the belt system.

At least a part of the first waist region is attached to a part of thesecond waist region by the closing system to hold the fluid-absorbentarticle in place and to form leg openings and the waist of thefluid-absorbent article. Preferably the fluid-absorbent article isprovided with a re-closable closing system.

The closing system is either re-sealable or permanent, including anymaterial suitable for such a use, e.g. plastics, elastics, films, foams,nonwoven substrates, woven substrates, paper, tissue, laminates, fiberreinforced plastics and the like, or combinations thereof. Preferablythe closing system includes flexible materials and works smooth andsoftly without irritating the wearer's skin.

One part of the closing elements is an adhesive tape, or comprises apair of laterally extending tabs disposed on the lateral edges of thefirst waist region. Tape tabs are typically attached to the front bodypanel and extend laterally from each corner of the first waistband.These tape tabs include an adhesive inwardly facing surface which istypically protected prior to use by a thin, removable cover sheet.

Suitable tape tabs may be formed of thermoplastic polymers such aspolyethylene, polyurethane, polystyrene, polycarbonate, polyester,ethylene vinyl acetate, ethylene vinyl alcohol, ethylene vinyl acetateacrylate or ethylene acrylic acid copolymers.

Suitable closing systems comprise further a hook portion of a hook andloop fastener and the target devices comprise the loop portion of a hookand loop fastener.

Suitable mechanical closing systems including a landing zone. Mechanicalclosing systems may fasten directly into the outer cover. The landingzone may act as an area of the fluid-absorbent article into which it isdesirable to engage the tape tabs. The landing zone may include a basematerial and a plurality of tape tabs. The tape tabs may be embedded inthe base material of the landing zone. The base material may include aloop material. The loop material may include a backing material and alayer of a nonwoven spunbond web attacked to the backing material.

Thus suitable landing zones can be made by spunbonding. Spunbondednonwovens are made from melt-spun fibers formed by extruding moltenthermoplastic material. Preferred is bioriented polypropylene (BOPP), orbrushed/closed loop in the case of mechanical closing systems.

Further, suitable mechanical closing systems including elastic unitsserving as a flexible waist band for fluid-absorbents articles, such aspants or pull-ups. The elastic units enabling the fluid-absorbentarticle to be pulled down by the wearer as e.g. a training pant.

Suitable pants-shaped fluid-absorbent article has front section, rearsection, crotch section, side sections for connecting the front and rearsections in lateral direction, hip section, elastic waist region andliquid-tight outer layer. The hip section is arranged around the waistof the user. The disposable pants-shaped fluid-absorbent article(pull-up) has favorable flexibility, stretchability, leak-proof propertyand fit property, hence imparts excellent comfort to the wearer.

Suitable pull-ups comprising thermoplastic films, sheets and laminateshaving a low modulus, good tear strength and high elastic recovery.

Suitable closing systems may further comprise elastomerics for theproduction of elastic areas within the fastening devices of thefluid-absorbent article. Elastomerics provide a conformable fit of thefluid-absorbent article to the wearer at the waist and leg openings,while maintaining adequate performance against leakage.

Suitable elastomerics are elastomeric polymers or elastic adhesivematerials showing vapor permeability and liquid barrier properties.Preferred elastomerics are retractable after elongation to a lengthequivalent to its original length.

Suitable closing systems further comprise a belt system, comprisingwaist-belt and leg-belts for flexibly securing the fluid-absorbentarticle on the body of the wearer and to provide an improved fit on thewearer. Suitable waist-belts comprising two elastic belts, a leftelastic belt, and a right elastic belt. The left elastic belt isassociated with each of the left angular edges. The right elastic beltassociated with each of the right angular edges. The left and right sidebelts are elastically extended when the absorbent garment is laid flat.Each belt is connected to and extends between the front and rear of thefluid-absorbent article to form a waist hole and leg holes.

Preferably the belt system is made of elastomerics, thus providing aconformable fit of the fluid-absorbent article and maintaining adequateperformance against leakage.

D. Fluid-Absorbent Article Construction

The present invention further relates to the joining of the componentsand layers, films, sheets, tissues or substrates mentioned above toprovide the fluid-absorbent article. At least two, preferably alllayers, films, sheets, tissues or substrates are joined.

Suitable fluid-absorbent articles include a single- or multiplefluid-absorbent core-system. Preferably fluid-absorbent articles includea single- or double fluid-absorbent core-system.

Suitable fluid-storage layers of the fluid-absorbent core comprisinghomogenous or inhomogeneous mixtures of fibrous materials comprisingwater-absorbent polymer particles homogeneously or inhomogeneouslydispersed in it. Suitable fluid-storage layers of the fluid-absorbentcore including a layered fluid-absorbent core-system comprisinghomogenous mixtures of fibrous materials and optionally comprisingwater-absorbent polymer particles, whereby each of the layers may beprepared from any fibrous material by means known in the art.

In order to immobilize the water-absorbent polymer particles, theadjacent layers are fixed by the means of thermoplastic materials,thereby building connections throughout the whole surface oralternatively in discrete areas of junction. For the latter case,cavities or pockets are built carrying the fluid-absorbent particles.The areas of junction may have a regular or irregular pattern, e.g.aligned with the longitudinal axis of the fluid-absorbent core or in apattern of polygons, e.g. pentagons or hexagons. The areas of junctionitself may be of rectangular, circular or squared shape with diametersbetween about 0.5 mm and 2 mm. Fluid-absorbent articles comprising areasof junction show a better wet strength.

The construction of the products chassis and the components containedtherein is made and controlled by the discrete application of hotmeltadhesives as known to people skilled in the art. Examples would be e.g.Dispomelt 505B, Dispomelt Cool 1101, as well as other specific functionadhesives manufactured by National Starch or Henkel.

The water-absorbent polymer particles and the fluid-absorbent articlesare tested by means of the test methods described below.

Methods

The measurements should, unless stated otherwise, be carried out at anambient temperature of 23±2° C. and a relative atmospheric humidity of50±10%. The water-absorbent polymers are mixed thoroughly before themeasurement.

Saline Flow Conductivity (SFC)

The saline flow conductivity is, as described in EP 0 640 330 A1,determined as the gel layer permeability of a swollen gel layer ofwater-absorbent polymer particles, although the apparatus described onpage 19 and in FIG. 8 in the aforementioned patent application wasmodified to the effect that the glass frit (40) is no longer used, theplunger (39) consists of the same polymer material as the cylinder (37)and now comprises 21 bores having a diameter of 9.65 mm each distributeduniformly over the entire contact surface. The procedure and theevaluation of the measurement remains unchanged from EP 0 640 330 A1.The flow rate is recorded automatically.

The saline flow conductivity (SFC) is calculated as follows:

SFC [cm³ s/g]=(Fg(t=0)×L0)/(dxAxWP),

where Fg(t=0) is the flow rate of NaCl solution in g/s, which isobtained by means of a linear regression analysis of the Fg(t) data ofthe flow determinations by extrapolation to t=0, L0 is the thickness ofthe gel layer in cm, d is the density of the NaCl solution in g/cm³, Ais the surface area of the gel layer in cm² and WP is the hydrostaticpressure over the gel layer in dyn/cm².

Free Swell Rate (FSR)

1.00 g (=W1) of the dry water-absorbent polymer particles is weighedinto a 25 ml glass beaker and is uniformly distributed on the base ofthe glass beaker. 20 ml of a 0.9% by weight sodium chloride solution arethen dispensed into a second glass beaker, the content of this beaker israpidly added to the first beaker and a stopwatch is started. As soon asthe last drop of salt solution is absorbed, confirmed by thedisappearance of the reflection on the liquid surface, the stopwatch isstopped. The exact amount of liquid poured from the second beaker andabsorbed by the polymer in the first beaker is accurately determined byweighing back the second beaker (=W2). The time needed for theabsorption, which was measured with the stopwatch, is denoted t. Thedisappearance of the last drop of liquid on the surface is defined astime t.

The free swell rate (FSR) is calculated as follows:

FSR [g/gs]=W2/(W1xt)

When the moisture content of the hydrogel-forming polymer is more than3% by weight, however, the weight W1 must be corrected for this moisturecontent.

Vortex

50.0±1.0 ml of 0.9% NaCl solution are added into a 100 ml beaker. Acylindrical stirrer bar (30×6 mm) is added and the saline solution isstirred on a stir plate at 60 rpm. 2.000±0.010 g of water-absorbentpolymer particles are added to the beaker as quickly as possible,starting a stop watch as addition begins. The stopwatch is stopped whenthe surface of the mixture becomes “still” that means the surface has noturbulence, and while the mixture may still turn, the entire surface ofparticles turns as a unit. The displayed time of the stopwatch isrecorded as Vortex time.

Morphology

Particle morphologies of the water-absorbent polymer particles wereinvestigated in the swollen state by microscope analysis. Approximately100 mg of the water-absorbent polymer particles were placed on a glassmicroscope slide. With a syringe, 0.9% aqueous NaCl solution was placedon the water-absorbent polymer particles to swell them. Solution wasconstantly refilled as it was absorbed by the particles. Care has to betaken that the water-absorbent polymer particles do not run dry. After30 min swelling time, the slide was put under the microscope (LeicaMacroscope Z16 APO, magnification 20×, backlighting by a Schott KL2500LCD cold light source, camera Leica DFC 420, all by Leica MicrosystemeVein ieb GmbH; Wetzlar; Germany) and 3 pictures were taken at differentparts of the sample.

Morphologies can be divided into there categories: Type 1 are particleswith one cavity having diameters from 0.4 to 2.5 mm, Type 2 areparticles with more than one cavity having diameters from 0.001 to 0.3mm, and Type 3 are solid particles with no visible cavity.

FIG. 9 shows a swollen particle of type 1 with a cavity having adiameter of 0.94 mm and FIG. 10 shows a swollen particle of type 2 withmore than 15 cavities having diameters from less than 0.03 to 0.13 mm.

The photograph is analyzed and the numbers of each category is recorded.Undefined or agglomerated particles are omitted from further evaluation.The individual results of the three photographs of each sample areaveraged.

Free Swell Gel Bed Permeability (GBP)

The method to determine the free swell gel bed permeability is describedin US 2005/0256757, paragraphs [0061] to [0075].

Particle Size Distribution

The particle size distribution of the water-absorbent polymer particlesis determined with the Camziser® image analysis system (RetschTechnology GmbH; Haan; Germany).

For determination of the average particle diameter and the particlediameter distribution the proportions of the particle fractions byvolume are plotted in cumulated form and the average particle diameteris determined graphically.

The average particle diameter (APD) here is the value of the mesh sizewhich gives rise to a cumulative 50% by weight.

The particle diameter distribution (PDD) is calculated as follows:

${{P\; D\; D} = \frac{x_{2} - x_{1}}{A\; P\; D}},$

wherein x₁ is the value of the mesh size which gives rise to acumulative 90% by weight and x₂ is the value of the mesh size whichgives rise to a cumulative 10% by weight.

Mean Sphericity

The mean sphericity is determined with the Camziser® image analysissystem (Retsch Technology GmbH; Haan; Germany) using the particlediameter fraction from 100 to 1,000 μm.

Moisture Content

The moisture content of the water-absorbent polymer particles isdetermined by the EDANA recommended test method No. WSP 230.2-05“Moisture Content”.

Centrifuge Retention Capacity (CRC)

The centrifuge retention capacity of the water-absorbent polymerparticles is determined by the EDANA recommended test method No. WSP241.2-05 “Centrifuge Retention Capacity”, wherein for higher values ofthe centrifuge retention capacity lager tea bags have to be used.

Absorbency Under High Load (AUHL)

The absorbency under high load of the water-absorbent polymer particlesis determined analogously to the EDANA recommended test method No. WSP242.2-05 “Absorption Under Pressure”, except using a weight of 49.2g/cm² instead of a weight of 21.0 g/cm².

Extractables

The level of extractable constituents in the water-absorbent polymerparticles is determined by the EDANA recommended test method No. WSP270.2-05 “Extractables”.

Wet SAP Shake Out (SAPLoss)

The wet SAP shake out of water-absorbent polymer particles is determinedusing a rectangle core sample having a size of 7 inch×4 inch (17.8cm×10.2 cm) that is cut from the center of a fluid-absorbent core. Theweight of the cut core sample is recorded as Dry Weight (W_(dry)). Thedry core sample is laid in a pan and 10 g of 0.9% NaCl solution per gramof Dry Weight are added to the core sample homogeneously. Five minutesafter all free liquid has been absorbed by the core sample, the wet coresample is weighted and recorded as Before Shake Wet Weight (W_(b-wet)).The wet core sample is carefully placed on top of an 850 micron U.S.A.standard testing sieve (VWR International LLC; Arlington Heights;U.S.A.). The sieve with the wet core sample is installed on a Retsch® AS200 sieve shaker (Retsch GmbH; Haan; Gemany) and shaken at a pre-setamplitude of 2.00 for 5 minutes. Next, the wet core sample is picked upon the short end and vertically transferred to a weighting pan. The wetcore sample is recorded as After Shake Wet Weight (W_(a-wet)). The wetSAP shake out (SAPLoss) is calculated as follows:

${{SAPLoss}\left\lbrack {{wt}.\%} \right\rbrack} = \frac{W_{b - {wet}} - W_{a - {wet}}}{W_{b - {wet}}}$

The EDANA test methods are obtainable, for example, from the EDANA,Avenue Eugene Plasky 157, B-1030 Brussels, Belgium.

EXAMPLES

Preparation of the Base Polymer

Example 1

The process was performed in a cocurrent spray drying plant with anintegrated fluidized bed (27) and an external fluidized bed (29) asshown in FIG. 1. The cylindrical part of the spray dryer (5) had aheight of 22 m and a diameter of 3.4 m. The internal fluidized bed (IFB)had a diameter of 2.0 m and a weir height of 0.4 m. The externalfluidized bed (EFB) had a length of 3.0 m, a width of 0.65 m and a weirheight of 0.5 m.

The drying gas was feed via a gas distributor (3) at the top of thespray dryer. The drying gas was partly recycled (drying gas loop) via abaghouse filter (9) and a condenser column (12). The drying gas wasnitrogen that comprises from 1% to 5% by volume of residual oxygen.Before start of polymerization the drying gas loop was filled withnitrogen until the residual oxygen was below 5% by volume. The gasvelocity of the drying gas in the cylindrical part of the spray dryer(5) was 0.59 m/s. The pressure inside the spray dryer was 4 mbar belowambient pressure.

The spray dryer outlet temperature was measured at three points aroundthe circumference at the end of the cylindrical part as shown in FIG. 3.Three single measurements (47) were used to calculate the averagecylindrical spray dryer outlet temperature. The drying gas loop washeated up and the dosage of monomer solution is started up. From thistime the spray dryer outlet temperature was controlled to 125° C. byadjusting the gas inlet temperature via the heat exchanger (20).

The product accumulated in the internal fluidized bed (27) until theweir height was reached. Conditioned internal fluidized bed gas having atemperature of 94° C. and a relative humidity of 38% was fed to theinternal fluidized bed (27) via line (25). The relative humidity wascontrolled by adding steam via line (23). The gas velocity of theinternal fluidized bed gas in the internal fluidized bed (27) was 0.8m/s. The residence time of the product was 44 min.

The spray dryer offgas was filtered in baghouse filter (9) and sent to acondenser column (12) for quenching/cooling. Excess water was pumped outof the condenser column (12) by controlling the (constant) filling levelinside the condenser column (12). The water inside the condenser column(12) was cooled by a heat exchanger (13) and pumped counter-current tothe gas via quench nozzles (11) so that the temperature inside thecondenser column (12) was 45° C. The water inside the condenser column(12) was set to an alkaline pH by dosing sodium hydroxide solution towash out acrylic acid vapors.

The condenser column offgas was split to the drying gas inlet pipe (1)and the conditioned internal fluidized bed gas (25). The gastemperatures were controlled via heat exchangers (20) and (22). The hotdrying gas was fed to the cocurrent spray dryer via gas distributor (3).The gas distributor (3) consists of a set of plates providing a pressuredrop of 5 to 10 mbar depending on the drying gas amount.

The product was discharged from the internal fluidized bed (27) viarotary valve (28) into external fluidized bed (29). Conditioned externalfluidized bed gas having a temperature of 55° C. was fed to the externalfluidized bed (29) via line (40). The external fluidized bed gas wasair. The gas velocity of the external fluidized bed gas in the externalfluidized bed (29) was 0.8 m/s. The residence time of the product was 14min.

The product was discharged from the external fluidized bed (29) viarotary valve (32) into sieve (33). The sieve (33) was used for sievingoff overs/lumps having a particle diameter of more than 850 μm.

The monomer solution was prepared by mixing first acrylic acid with3-tuply ethoxylated glycerol triacrylate (internal crosslinker) andsecondly with 37.3% by weight sodium acrylate solution. The temperatureof the resulting monomer solution was controlled to 10° C. by using aheat exchanger and pumping in a loop. A filter unit having a mesh sizeof 250 μm was used in the loop after the pump. The initiators weremetered into the monomer solution upstream of the dropletizer by meansof static mixers (41) and (42) via lines (43) and (44) as shown inFIG. 1. Sodium peroxodisulfate solution having a temperature of 20° C.was added via line (43) and2,2′-azobis[2-(2-imidazolin-2-yl)pro-pane]dihydrochloride solutionhaving a temperature of 5° C. was added via line (44). Each initiatorwas pumped in a loop and dosed via control valves to each dropletizerunit. A second filter unit having a mesh size of 100 μm was used afterthe static mixer (42). For dosing the monomer solution into the top ofthe spray dryer three dropletizer units were used as shown in FIG. 4.

A dropletizer unit consisted of an outer pipe (51) having an opening forthe dropletizer cassette (53) as shown in FIG. 5. The dropletizercassette (53) was connected with an inner pipe (52). The inner pipe (53)having a PTFE block (54) at the end as sealing can be pushed in and outof the outer pipe (51) during operation of the process for maintenancepurposes.

The temperature of the dropletizer cassette (61) was controlled to 25°C. by water in flow channels (59) as shown in FIG. 6. The dropletizercassette had 200 bores having a diameter of 200 μm and a bore separationof 15 mm. The dropletizer cassette (61) consisted of a flow channel (60)having essential no stagnant volume for homogeneous distribution of thepremixed monomer and initiator solutions and two droplet plates (57).Thedroplet plates (57) had an angled configuration with an angle of 10°.Each droplet plate (57) was made of stainless steel and had a length of500 mm, a width of 25 mm, and a thickness of 1 mm.

The feed to the spray dryer consisted of 10.25% by weight of acrylicacid 32.75% by weigh of sodium acrylate, 0.070% by weight of 3-tuplyethoxylated glycerol triacrylate (approx. 85% strength by weight), 0.12%by weight of 2,2′-azobis[2-(2-imidazolin-2-yl)-propane]dihydrochloridesolution (15% by weigh in water), 0.12% by weight of sodiumperoxodisulfate solution (15% by weight in water) and water. The degreeof neutralization was 71%. The feed per bore was 2.0 kg/h.

The polymer particles exhibit the following features and absorptionprofile:

-   CRC of 31.0 g/g-   SFC of 14×10⁻⁷ cm³ s/g-   AUHL of 20.3 g/g-   GBP of 5 Darcies    The resulting polymer particles had a particle diameter distribution    of 0.55 and a mean sphericity of 0.92.

Example 2

Example 1 was repeated, except that the separation of the bores was 11mm. For dosing the monomer solution into the top of the spray dryerthree dropletizer unit with 267 bores having a diameter of 200 μm wereused.

The conditioned internal fluidized bed gas had a temperature of 98° C.and a relative humidity of 45%.

The feed to the spray dryer consisted of 10.25% by weight of acrylicacid 32.75% by weigh of sodium acrylate, 0.039% by weight of 3-tuplyethoxylated glycerol triacrylate (approx. 85% strength by weight), 0.12%by weight of 2,2′-azobis[2-(2-imidazolin-2-yl)-propane]dihydrochloridesolution (15% by weight in water), 0.12% by weight of sodiumperoxodisulfate solution (15% by weight in water) and water. The feedper bore was 1.5 kg/h.

The polymer particles exhibit the following features and absorptionprofile:

-   CRC of 44.5 g/g-   AUHL of 9.9 g/g-   SFC of 1×10⁻⁷ cm³ s/g

The resulting polymer particles had a particle diameter distribution of0.66 and a mean sphericity of 0.93.

Coating of the Base Polymer

Example 3

800g of the water-absorbent polymer particles prepared in example 1 wereadded in a mechanical plough share mixer (Pflugschar® Mischer Typ M5;Gebr. Lödige Maschinenbau GmbH; Paderborn; Germany) at room temperature.At a stirring speed of 200 rpm, the water-absorbent polymer particleswere coated with 3.8 by weight of aluminum sulfate solution (26.8% byweight in water) within 4 minutes. The speed of the mixer was reducedafter coating to 60 rpm and the product was mixed for 5 more minutes atthese conditions. After removal of the product from the mixer, it wassieved over an 850 μm screen to remove potential agglomerates.

The polymer particles exhibit the following features and absorptionprofile:

-   CRC of 31.0 g/g-   SFC of 31×10⁻⁷ cm³ s/g-   AUHL of 19.8 g/g-   GBP of 60 Darcies-   Moisture content of 11.7 wt. %

Postcrosslinking of the Base Polymer

Example 4

1 kg of the water-absorbent polymer particles prepared in example 2 wereput into a laboratory ploughshare mixer with a heated jacket (model M 5;manufactured by Gebrüder Lödige Maschinenbau GmbH; Paderborn; Germany).A postcrosslinker solution was prepared by mixing 1.00 g of Denacol® EX512 (polyglycerol polyglycidyl ether; obtained from Nagase ChemteXCorporation; Osaka; Japan), 7.5 g of propylene glycol, and 15 g ofdeionized water, into a beaker. At a mixer speed of 450 rpm, thepostcrosslinker solution was added by a spray nozzle to the polymerpowder over a three minute time period at room temperature. The mixerwas then stopped, product sticking to the wall of the mixing vessel wasscraped off (and re-united with the bulk), and mixing was continued fortwo more minutes at 450 rpm. The temperature of the product was thenraised to 160° C. by heating the jacket of the mixer. The product waskept at this temperature for 15 minutes at a mixer speed of 80 rpm.After cooling down of the mixer, the product was discharged, sifted at150 to 850 μm and characterized as follows:

-   CRC of 41.1 g/g-   SFC of 7×10⁻⁷ cm³ s/g-   AUHL of 29.3 g/g-   Extractables of 3.2 wt. %-   FSR of 0.21 g/gs-   Vortex of 94.7 s

Preparation of the Fluid-Absorbent Cores

Example 5

A first substrate layer was laid on a flat cardboard and covered with apattern template. The substrate was a commercially available 17 gsmforming tissue (Cellu Tissue Holdings, Inc.; East Hartford; U.S.A.)having a size of 14.5 inch×4.5 inch (36.8 cm×11.4 cm).

The template was a commercially available stainless steel plate havingsquare end slots and an open area of 40% (Direct Metals Company, LLC;Kennesaw; U.S.A.). The template had a size of 10 inch×14 inch (25.4cm×35.6 cm). The slots had a size of ¼ inch×⅜ inch (0.64 cm×0.95 cm) andwere side staggered having end and side bars of 3/16 inch (0.48 cm).

11 g of water-absorbent polymer particles prepared in example 3 wereadded as evenly as possible onto the template and then evenlydistributed with a smooth rubber blade to create a pattern ofwater-absorbent polymer particles on the first substrate layer.

A piece of a commercially available pressure sensitive adhesive having20 gsm (BASF Corporation; Monaca; U.S.A.) on a release paper wastransferred onto a second substrate layer (corresponding to 0.84 gadhesive). Next, the template on the first substrate layer was carefullyremoved and the second substrate layer was placed on the top of thefirst substrate layer with the adhesive side of the second substratelayer facing the top side with the water-absorbent polymer particles ofthe first substrate layer.

The fluid-absorbent core was transferred with the cardboard into aCarver® Press model Auto Series 4425.4DI0A01 (Carver Inc.; Wabash;U.S.A.). The press was pre-set to 10,000 lbs (corresponding to 1,054kPa) and immediately stopped once the pre-set pressure was reached.

The resulting fluid-absorbent core was analyzed, the results aresummarized in table 1.

Example 6

Example 5 was repeated, except that the water-absorbent polymerparticles prepared in example 4 were used. The resulting fluid-absorbentcore was analyzed, the results are summarized in table 1.

Example 7

Example 5 was repeated, except that the substrate layers werecommercially available 15 gsm nonwoven (AVGOL American Inc.; Mocksville;U.S.A.) having a size of 14.5 inch×4.5 inch (36.8 cm×11.4 cm). Theresulting fluid-absorbent core was analyzed, the results are summarizedin table 1.

Example 8

Example 7 was repeated, except that the water-absorbent polymerparticles prepared in example 4 were used. The resulting fluid-absorbentcore was analyzed, the results are summarized in table 1.

Example 9

Example 7 was repeated, except that the pattern template was acommercially available perforated plastic piece having round holes(United States Plastic Corporation; Lima Ohio; U.S.A.). The template hada size of 4.5 inch×14 inch (11.4 cm×35.6 cm) and a thickness of ⅛ inch(0.3 cm). The holes had a diameter of ¼ inch (0.64 cm) and were sidestaggered (every other hole was taped off) having end and side bars of ½inch (1.3 cm). The resulting fluid-absorbent core was analyzed, theresults are summarized in table 1.

Example 10

Example 9 was repeated, except that the water-absorbent polymerparticles prepared in example 4 were used. The resulting fluid-absorbentcore was analyzed, the results are summarized in table 1.

TABLE 1 Results of the wet SAP shake out procedure water-absorbentpattern Example polymer particles substrate template SAP Loss Example 5Example 3 tissue paper square slots  6.2 wt. % Example 6 Example 4tissue paper square slots  2.1 wt. % ASAP ® 531T tissue paper squareslots 65.2 wt. % Hysorb ® B7055 tissue paper square slots 42.1 wt. %Hysorb ® T8760 tissue paper square slots 17.5 wt. % Example 7 Example 3nonwoven square slots  6.4 wt. % Example 8 Example 4 nonwoven squareslots  4.8 wt. % ASAP ® 531T nonwoven square slots 50.1 wt. % Hysorb ®B7055 nonwoven square slots 47.2 wt. % Hysorb ® T8760 nonwoven squareslots 16.8 wt. % Example 9 Example 3 nonwoven round holes  4.5 wt. %Example Example 4 nonwoven round holes  8.1 wt. % 10 ASAP ® 531Tnonwoven round holes 31.3 wt. % Hysorb ® B7055 nonwoven round holes 21.0wt. % Hysorb ® T8760 nonwoven round holes 13.6 wt. %

ASAP® 531T, Hysorb® B7055, and Hysorb® T8760 are commercially availablewater-absorbent polymer particles (BASF SE; Ludwigshafen; Germany)prepared by customary solution polymerization.

1. A fluid-absorbent core comprising a substrate layer, at least 75% by weight of water-absorbent polymer particles, and an adhesive, wherein the water-absorbent polymer particles have a mean sphericity from 0.86 to 0.99 and a wet SAP shake out of water-absorbent polymer particles out of the fluid-absorbent core is less than 10% by weight.
 2. The fluid-absorbent core according to claim 1, wherein the fluid-absorbent core comprises at least 80% by weight of water-absorbent polymer particles.
 3. The fluid-absorbent core according to claim 1, wherein the fluid-absorbent core comprises not more than 15% by weight of the adhesive.
 4. The fluid-absorbent core according to claims 1, wherein the wet SAP shake out of water-absorbent polymer particles out of the fluid-absorbent core is less than 8% by weight.
 5. The fluid-absorbent core according to claim 1, wherein the wet SAP shake out of water-absorbent polymer particles out of the fluid-absorbent core is less than 5% by weight.
 6. The fluid-absorbent core according to claim 1, wherein the adhesive is a pressure sensitive adhesive.
 7. The fluid-absorbent core according to claim 1, wherein the substrate layer is a nonwoven layer or a tissue paper.
 8. The fluid-absorbent core according to claim 1, wherein the fluid-absorbent core comprises at least two layers of water-absorbent polymer particles.
 9. The fluid-absorbent core according to claim 1, wherein the water-absorbent polymer particles are placed in discrete regions.
 10. The fluid-absorbent core according to claim 1, wherein the water-absorbent polymer particles have a particle diameter distribution is less than 0.7.
 11. The fluid-absorbent core according to claim 1, wherein a ratio of water-absorbent polymer particles having one cavity to water-absorbent polymer particles having more than one cavity is less than 1.0.
 12. The fluid-absorbent core according to claim 1, wherein the water-absorbent polymer particles have a centrifuge retention capacity of at least 30 g/g, an absorption under high load of at least 15 g/g, and a saline flow conductivity of at least 5×10⁻⁷ cm³ s/g.
 13. The fluid-absorbent core according to claim 1, wherein the water-absorbent polymer particles have a centrifuge retention capacity of at least 20 g/g, an absorption under high load of at least 15 g/g, and a saline flow conductivity of at least 80×10⁻⁷ cm³ s/g.
 14. The fluid-absorbent core according to claim 1, wherein the water-absorbent polymer particles have a centrifuge retention capacity of at least 20 g/g and a free swell gel bed permeability of at least 20 Darcies.
 15. A fluid-absorbent article, comprising (A) an upper liquid-pervious layer, (B) a lower liquid-impervious layer and (C) a fluid-absorbent core according to claim 1 between the layer (A) and the layer (B), (D) an optional acquisition-distribution layer between (A) and (C), (E) an optional tissue layer disposed immediately above and/or below (C), and (F) other optional components. 